ai 


THE  ORIGIN  OF  SPECIES 

VOL.   II 


THE  ORIGIN  OF  SPECIES 

BY  MEANS  OF  NATURAL  SELECTION 


OR  THE   PRESERVATION  OF  FAVORED 
RACES    IN    THE  'STRUGGLE    FOR   LIFE 


BY  CHARLES  DARWIN 

M.  A.,    LL.  D.,   F.  R.S. 


WITH   ADDITIONS   AND    CORRECTIONS 
FROM  SIXTH    AND   LAST    ENGLISH    EDITION 


IN  TWO   VOLUMES 
VOL.    II 


NEW    YORK 

D.    APPLETON    AND    COMPANY 
1808 


Authorized  Edition. 


CONTENTS  OF  VOL.  II. 


CHAPTER  IX. 

HYBRIDISM. 

Distinction  between  the  sterility  of  first  crosses  and  of  hybrids- 
Sterility  various  in  degree,  not  universal,  affected  by  close  in- 
terbreeding, removed  by  domestication — Laws  governing  the 
sterility  of  hybrids — Sterility  not  a  special  endowment,  but 
incidental  on  other  differences,  not  accumulated  by  natural 
selection— Causes  of  the  sterility  of  first  crosses  and  of  hybrids 
— Parallelism  between  the  effects  of  changed  conditions  of  life 
and  of  crossing — Dimorphism  and  trimorphism — Fertility  of 
varieties  when  crossed  and  of  their  mongrel  offspring  not  uni- 
versal—Hybrids and  mongrels  compared  independently  of  their 
fertility— Summary Page  1 

CHAPTER  X. 

ON  THE  IMPERFECTION  OF  THE  GEOLOGICAL  RECORD. 

On  the  absence  of  intermediate  varieties  at  the  present  day — On 
the  nature  of  extinct  intermediate  varieties ;  on  their  number — 
On  the  lapse  of  time,  as  inferred  from  the  rate  of  denudation 
and  of  deposition— On  the  lapse  of  time  as  estimated  by  years 
— On  the  poorness  of  our  palaeontological  collections — On  the 
intermittence  of  geological  formations — On  the  denudation  of 
granitic  areas — On  the  absence  of  intermediate  varieties  in  any 
one  formation— On  the  sudden  appearance  of  groups  of  species 
— On  their  sudden  appearance  in  the  lowest  known  fossiliferous 
strata— Antiquity  of  the  habitable  earth  ....  48 


vi  CONTENTS. 


CHAPTER  XL 

ON  THE  GEOLOGICAL  SUCCESSION  OF  ORGANIC   BEINGS. 

On  the  slow  and  successive  appearance  of  new  species — On  their 
different  rates  of  change — Species  once  lost  do  not  reappear — 
Groups  of  species  follow  the  same  general  rules  in  their  ap- 
pearance and  disappearance  as  do  single  species — On  extinction 
— On  simultaneous  changes  in  the  forms  of  life  throughout  the 
world — On  the  affinities  of  extinct  species  to  each  other  and  to 
living  species — On  the  state  of  development  of  ancient  forms — 
On  the  succession  of  the  same  types  within  the  same  areas — 
Summary  of  preceding  and  present  chapter  .  .  Page  89 


CHAPTER  XII. 

GEOGRAPHICAL  DISTRIBUTION. 

Present  distribution  cannot  be  accounted  for  by  differences  in 
physical  conditions — Importance  of  barriers — Affinity  of  the 
productions  of  the  same  continent — Centres  of  creation — Means 
of  dispersal  by  changes  of  climate  and  of  the  level  of  the  land, 
and  by  occasional  means — Dispersal  during  the  Glacial  period 
—Alternate  Glacial  periods  in  the  North  and  South  .  .  129 


CHAPTER  XIII. 

GEOGRAPHICAL  DISTRIBUTION — Continued. 

Distribution  of  fresh-water  productions — On  the  inhabitants  of 
oceanic  islands — Absence  of  Batrachians  and  of  terrestrial  Mam- 
mals— On  the  relation  of  the  inhabitants  of  islands  to  those  of 
the  nearest  mainland — On  colonisation  from,the  nearest  source 
with  subsequent  modification— Summary  of  the  last  and  present 
chapter 171 


CONTENTS. 


CHAPTER  XIV. 

MUTUAL    AFFINITIES    OF    ORGANIC    BEINGS  :     MORPHOLOGY  : 
EMBRYOLOGY :    RUDIMENTARY   ORGANS. 

CLASSIFICATION,  groups  subordinate  to  groups — Natural  system — 
Rules  and  difficulties  in  classification,  explained  on  the  theory 
of  descent  with  modification — Classification  of  varieties — De- 
scent always  used  in  classification— Analogical  or  adaptive  char- 
acters—Affinities, general,  complex,  and  radiating — Extinction 
separates  and  defines  groups — MORPHOLOGY,  between  members 
of  the  same  class,  between  parts  of  the  same  individual — 
EMBRYOLOGY,  laws  of,  explained  by  variations  not  super- 
vening at  an  early  age,  and  being  inherited  at  a  correspond- 
ing age— RUDIMENTARY  ORGANS  :  their  origin  explained— Sum- 
mary   Page  202 

CHAPTER  XV. 

RECAPITULATION   AND   CONCLUSION. 

Recapitulation  of  the  objections  to  the  theory  of  Natural  Selection 
— Recapitulation  of  the  general  and  special  circumstances  in  its 
favour — Causes  of  the  general  belief  in  the  immutability  of 
species— How  far  the  theory  of  Natural  Selection  may  be  ex- 
tended—Effects of  its  adoption  on  the  study  of  Natural  History 
— Concluding  remarks 267 

GLOSSARY  OF  SCIENTIFIC  TERMS 307 

INDEX  .  .  323 


ORIGIN  OF  SPECIES. 


CHAPTER   IX. 

HYBRIDISM. 

Distinction  between  the  sterility  of  first  crosses  and  of  hybrids- 
Sterility  various  in  degree,  not  universal,  affected  by  close  in- 
terbreeding, removed  by  domestication — Laws  governing  the 
sterility  of  hybrids — Sterility  not  a  special  endowment,  but 
incidental  on  other  differences,  not  accumulated  by  natural 
selection— Causes  of  the  sterility  of  first  crosses  and  of  hybrids 
— Parallelism  between  the  effects  of  changed  conditions  of  life 
and  of  crossing — Dimorphism  and  trimorphism — Fertility  of 
varieties  when  crossed  and  of  their  mongrel  offspring  not  uni- 
versal—Hybrids and  mongrels  compared  independently  of  their 
fertility— Summary. 

THE  view  commonly  entertained  by  naturalists  is 
that  species,  when  intercrossed,  have  been  specially  en- 
dowed with  sterility,  in  order  to  prevent  their  confusion. 
This  view  certainly  seems  at  first  highly  probable,  for 
species  living  together  could  hardly  have  been  kept  dis- 
tinct had  they  been  capable  of  freely  crossing.  The 
subject  is  in  many  ways  important  for  us,  more  especial- 
ly as  the  sterility  of  species  when  first  crossed,  and  that 
of  their  hybrid  offspring,  cannot  have  been  acquired,  as  I 
shall  show,  by  the  preservation  of  successive  profitable 
1 


2  HYBRIDISM.  [CHAP.  IX. 

degrees  of  sterility.  It  is  an  incidental  result  of  dif- 
ferences in  the  reproductive  systems  of  the  parent- 
species. 

In  treating  this  subject,  two  classes  of  facts,  to  a 
large  extent  fundamentally  different,  have  generally 
been  confounded;  namely,  the  sterility  of  species  when 
first  crossed,  and  the  sterility  of  the  hybrids  produced 
from  them. 

Pure  species  have  of  course  their  organs  of  reproduc- 
tion in  a  perfect  condition,  yet  when  intercrossed  they 
produce  either  few  or  no  offspring.  Hybrids,  on  the 
other  hand,  have  their  reproductive  organs  functionally 
impotent,  as  may  be  clearly  seen  in  the  state  of  the 
male  element  in  both  plants  and  animals;  though  the 
formative  organs  themselves  are  perfect  in  structure,  as 
far  as  the  microscope  reveals.  In  the  first  case  the  two 
sexual  elements  which  go  to  form  the  embryo  are  per-' 
feet;  in  the  second  case  they  are  either  not  at  all  de- 
veloped, or  are  imperfectly  developed.  This  distinc- 
tion is  important,  when  the  cause  of  the  sterility,  which 
is  common  to  the  two  cases,  has  to  be  considered.  The 
distinction  probably  has  been  slurred  over,  owing  to  the 
sterility  in  both  cases  being  looked  on  as  a  special  en- 
dowment, beyond  the  province  of  our  reasoning 
powers. 

The  fertility  of  varieties,  that  is  of  the  forms  known 
or  believed  to  be  descended  from  common  parents,  when 
crossed,  and  likewise  the  fertility  of  their  mongrel  off- 
spring, is,  with  reference  to  my  theory,  of  equal  im- 
portance with  the  sterility  of  species;  for  it  seems  to 
make  a  broad  and  clear  distinction  between  varieties 
and  species. 

Degrees  of  Sterility. — First,  for  the  sterility  of  spe- 


CHAP.  IX.]  DEGREES  OP  STERILITY.  ,        3 

cies  when  crossed  and  of  their  hybrid  offspring.  It  is 
impossible  to  study  the  several  memoirs  and  works  of 
those  two  conscientious  and  admirable  observers,  Kol- 
reuter  and  Gartner,  who  almost  devoted  their  lives  to 
this  subject,  without  being  deeply  impressed  with  the 
high  generality  of  some  degree  of  sterility.  Kolreuter 
makes  the  rule  universal;  but  then  he  cuts  the  knot, 
for  in  ten  cases  in  which  he  found  two  forms,  considered 
by  most  authors  as  distinct  species,  quite  fertile  to- 
gether, he  unhesitatingly  ranks  them  as  varieties.  Gart- 
ner, also,  makes  the  rule  equally  universal;  and  he  dis- 
putes the  entire  fertility  of  Kolreuter's  ten  cases.  But 
in  these  and  in  many  other  cases,  Gartner  is  obliged 
carefully  to  count  the  seeds,  in  order  to  show  that  there 
is  any  degree  of  sterility.  He  always  compares  the 
maximum  number  of  seeds  produced  by  two  species 
when  first  crossed,  and  the  maximum  produced  by  their 
hybrid  offspring,  with  the  average  number  produced  by 
both  pure  parent-species  in  a  state  of  nature.  But 
causes  of  serious  error  here  intervene:  a  plant,  to  be 
hybridised,  must  be  castrated,  and,  what  is  often  more 
important,  must  be  secluded  in  order  to  prevent  pollen 
being  brought  to  it  by  insects  from  other  plants. 
Nearly  all  the  plants  experimented  on  by  Gartner  were 
potted,  and  were  kept  in  a  chamber  in  his  house.  That 
these  processes  are  often  injurious  to  the  fertility  of  a 
plant  cannot  be  doubted;  for  Gartner  gives  in  his  table 
about  a  score  of  cases  of  plants  which  he  castrated,  and 
artificially  fertilised  with  their  own  pollen,  and  (ex- 
cluding all  cases  such  as  the  Leguminosa?,  in  which  there 
is  an  acknowledged  difficulty  in  the  manipulation) 
half  of  these  twenty  plants  had  their  fertility  in  some 
degree  impaired.  Moreover,  as  Gartner  repeatedly 


4  HYBRIDISM.  [CHAP.  IX. 

crossed  some  forms,  such  as  the  common  red  and 
blue  pimpernels  (Anagallis  arvensis  and  ccerulea), 
which  the  best  botanists  rank  as  varieties,  and  found 
them  absolutely  sterile,  we  may  doubt  whether  many 
species  are  really  so  sterile,  when  intercrossed,  as  he  be- 
lieved. 

It  is  certain,  on  the  one  hand,  that  the  sterility  of 
various  species  when  crossed  is  so  different  in  degree 
and  graduates  away  so  insensibly,  and,  on  the  other 
hand,  that  the  fertility  of  pure  species  is  so  easily 
affected  by  various  circumstances,  that  for  all  practical 
purposes  it  is  most  difficult  to  say  where  perfect  fertility 
ends  and  sterility  begins.  I  think  no  better  evidence 
of  this  can  be  required  than  that  the  two  most  ex- 
perienced observers  who  have  ever  lived,  namely  K61- 
reuter  and  Gartner,  arrived  at  diametrically  opposite 
conclusions  in  regard  to  some  of  the  very  same  forms. 
It  is  also  most  instructive  to  compare — but  I  have  not 
space  here  to  enter  on  details — the  evidence  advanced 
by  our  best  botanists  on  the  question  whether  certain 
doubtful  forms  should  be  ranked  as  species  or  varieties, 
with  the  evidence  from  fertility  adduced  by  different 
hybridisers,  or  by  the  same  observer  from  experiments 
made  during  different  years.  It  can  thus  be  shown 
that  neither  sterility  nor  fertility  affords  any  certain 
distinction  between  species  and  varieties.  The  evidence 
from  this  source  graduates  away,  and  is  doubtful  in  the 
same  degree  as  is  the  evidence  derived  from  other  con- 
stitutional and  structural  differences. 

In  regard  to  the  sterility  of  hybrids  in  successive 
generations;  though  Gartner  was  enabled  io  rear  some 
hybrids,  carefully  guarding  them  from  a  cross  with 
either  pure  parent,  for  six  or  seven,  and  in  one  case  for 


CHAP.  IX.]  DEGREES  OP  STERILITY.  5 

ten  generations,  yet  he  asserts  positively  that  their  fer- 
tility never  increases,  but  generally  decreases  greatly  and 
suddenly.  With  respect  to  this  decrease,  it  may  first  be 
noticed  that  when  any  deviation  in  structure  or  constitu- 
tion is  common  to  both  parents,  this  is  often  transmitted 
in  an  augmented  degree  to  the  offspring;  and  both  sexual 
elements  in  hybrid  plants  are  already  affected  in  some 
degree.  -But  I  believe  that  their  fertility  has  been  di- 
minished in  nearly  all  these  cases  by  an  independent 
cause,  namely,  by  too  close  interbreeding.  I  have  made 
so  many  experiments  and  collected  so  many  facts,  show- 
ing on  the  one  hand  that  an  occasional  cross  with  a  dis- 
tinct individual  or  variety  increases  the  vigour  and  fer- 
tility of  the  offspring,  and  on  the  other  hand  that  very 
close  interbreeding  lessens  their  vigour  and  fertility, 
that  I  cannot  doubt  the  correctness  of  this  conclusion. 
Hybrids  are  seldom  raised  by  experimentalists  in  great 
numbers;  and  as  the  parent-species,  or  other  allied 
hybrids,  generally  grow  in  the  same  garden,  the  visits  of 
insects  must  be  carefully  prevented  during  the 
flowering  season:  hence  hybrids,  if  left  to  themselves, 
will  generally  be  fertilised  during  each  generation  by 
pollen  from  the  same  flower;  and  this  would  probably 
be  injurious  to  their  fertility,  already  lessened  by  their 
hybrid  origin.  I  am  strengthened  in  this  conviction 
by  a  remarkable  statement  repeatedly  made  by  Gartner, 
namely,  that  if  even  the  less  fertile  hybrids  be  artificially 
fertilised  with  hybrid  pollen  of  the  same  kind,  their 
fertility,  notwithstanding  the  frequent  ill  effects  from 
manipulation,  sometimes  decidedly  increases,  and  goes 
on  increasing.  Now,  in  the  process  of  artificial  fertilisa- 
tion, pollen  is  as  often  taken  by  chance  (as  I  know  from 
my  own  experience)  from  the  anthers  of  another  flower, 


6  HYBRIDISM.  [CHAP.  IX. 

as  from  the  anthers  of  the  flower  itself  which  is  to  be  fer- 
tilised; so  that  a  cross  between  two  flowers,  though 
probably  often  on  the  same  plant,  would  be  thus  effected. 
Moreover,  whenever  complicated  experiments  are  in 
progress,  so  careful  an  observer  as  Gartner  would  have 
castrated  his  hybrids,  and  this  would  have  ensured  in 
each  generation  a  cross  with  pollen  from  a  distinct 
flower,  either  from  the  same  plant  or  from  another 
plant  of  the  same  hybrid  nature.  And  thus,  the  strange 
fact  of  an  increase  of  fertility  in  the  successive  genera- 
tions of  artificially  fertilised  hybrids,  in  contrast  with 
those  spontaneously  self -fertilised,  may,  as  I  believe,  be 
accounted  for  by  too  close  interbreeding  having  been 
avoided. 

Now  let  us  turn  to  the  results  arrived  at  by  a  third 
most  experienced  hybridiser,  namely,  the  Hon.  and  Rev. 
W.  Herbert.  He  is  as  emphatic  in  his  conclusion  that 
some  hybrids  are  perfectly  fertile — as  fertile  as  the  pure 
parent-species — as  are  Kolreuter  and  Gartner  that  some 
degree  of  sterility  between  distinct  species  is  a  universal 
law  of  nature.  He  experimented  on  some  of  the  very 
same  species  as  did  Gartner.  The  difference  in  their 
results  may,  I  think,  be  in  part  accounted  for  by 
Herbert's  great  horticultural  skill,  and  by  his  having 
hot-houses  at  his  command.  Of  his  many  important 
statements  I  will  here  give  only  a  single  one  as  an  ex- 
ample, namely,  that  "  every  ovule  in  a  pod  of  Crinum 
capense  fertilised  by  C.  revolutum  produced  a  plant, 
which  I  never  saw  to  occur  in  a  case  of  its  natural  fecun- 
dation." So  that  here  we  have  perfect  or  even  more 
than  commonly  perfect  fertility,  in  a  first  cross  between 
two  distinct  species. 

This  case  of  the  Crinum  leads  me  to  refer  to  a 


CHAP.  IX.]  DEGREES  OF  STERILITY.  7 

singular  fact,  namely,  that  individual  plants  of  certain 
species  of  Lobelia,  Verbascum  and  Passiflora,  can  easily 
be  fertilised  by  pollen  from  a  distinct  species,  but  not 
by  pollen  from  the  same  plant,  though  this  pollen  can 
be  proved  to  be  perfectly  sound  by  fertilising  other 
plants  or  species.  In  the  genus  Hippeastrum,  in  Cory- 
dalis  as  shown  by  Professor  Hildebrand,  in  various  or- 
chids as  shown  by  Mr.  Scott  and  Fritz  Miiller,  all  the 
individuals  are  in  this  peculiar  condition.  So  that  with 
some  species,  certain  abnormal  individuals,  and  in  other 
species  all  the  individuals,  can  actually  be  hybridised 
much  more  readily  than  they  can  be  fertilised  by  pollen 
from  the  same  individual  plant!  To  give  one  instance, 
a  bulb  of  Hippeastrum  aulicum  produced  four  flowers; 
three  were  fertilised  by  Herbert  with  their  own  pollen, 
and  the  fourth  was  subsequently  fertilised  by  the  pollen 
of  a  compound  hybrid  descended  from  three  distinct 
species:  the  result  was  that  "  the  ovaries  of  the  three 
first  flowers  soon  ceased  to  grow,  and  after  a  few  days 
perished  entirely,  whereas  the  pod  impregnated  by  the 
pollen  of  the  hybrid  made  vigorous  growth  and  rapid 
progress  to  maturity,  and  bore  good  seed,  which  vege- 
tated freely."  Mr.  Herbert  tried  similar  experiments 
during  many  years,  and  always  with  the  same  result. 
These  cases  serve  to  shoAV  on  what  slight  and  mysterious 
causes  the  lesser  or  greater  fertility  of  a  species  some- 
times depends. 

The  practical  experiments  of  horticulturists,  though 
not  made  with  scientific  precision,  deserve  some  notice. 
It  is  notorious  in  how  complicated  a  manner  the  species 
of  Pelargonium,  Fuchsia,  Calceolaria,  Petunia,  Rhodo- 
dendron, &c.,  have  been  crossed,  yet  many  of  these 
hybrids  seed  freely.  For  instance,  Herbert  asserts  that 


8  HYBRIDISM.  [CHAP.  IX. 

a  hybrid  from  Calceolaria  integrifolia  and  plantaginea, 
species  most  widely  dissimilar  in  general  habit,  "re- 
produces itself  as  perfectly  as  if  it  had  been  a  natural 
species  from  the  mountains  of  Chili."  I  have  taken 
some  pains  to  ascertain  the  degree  of  fertility  of  some 
of  the  complex  crosses  of  Rhododendrons,  and  I  am 
assured  that  many  of  them  are  perfectly  fertile.  Mr. 
C.  Noble,  for  instance,  informs  me  that  he  raises  stocks 
for  grafting  from  a  hybrid  between  Rhod.  ponticum  and 
catawbiense,  and  that  this  hybrid  "  seeds  as  freely  as  it 
is  possible  to  imagine."  Had  hybrids  when  fairly 
treated,  always  gone  on  decreasing  in  fertility  in  each 
successive  generation,  as  Gartner  believed  to  be  the 
case,  the  fact  would  have  been  notorious  to  nursery- 
men. Horticulturists  raise  large  beds  of  the  same  hy- 
brid, and  such  alone  are  fairly  treated,  for  by  insect 
agency  the  several  individuals  are  allowed  to  cross  freely 
with  each  other,  and  the  injurious  influence  of  close 
interbreeding  is  thus  prevented.  Any  one  may  readily 
convince  himself  of  the  efficiency  of  insect-agency  by 
examining  the  flowers  of  the  more  sterile  kinds  of  hy- 
brid Rhododendrons,  which  produce  no  pollen,  for  he 
will  find  on  their  stigmas  plenty  of  pollen  brought  from 
other  flowers. 

In  regard  to  animals,  much  fewer  experiments  have 
been  carefully  tried  than  with  plants.  If  our  systematic 
arrangements  can  be  trusted,  that  is,  if  the  genera  of 
animals  are  as  distinct  from  each  other  as  are  the  genera 
of  plants,  then  we  may  infer  that  animals  more  widely 
distinct  in  the  scale  of  nature  can  be  crossed  more  easily 
than  in  the  case  of  plants;  but  the  hybrids  themselves 
'are,  I  think,  more  sterile.  It  should,  however,  be  borne 
in  mind  that,  owing  to  few  animals  breeding  freely  under 


CHAP.  IX.]  DEGREES  OF  STERILITY.  9 

confinement,  few  experiments  have  been  fairly  tried:  for 
instance,  the  canary-bird  has  been  crossed  with  nine  dis- 
tinct species  of  finches,  but,  as  not  one  of  these  breeds 
freely  in  confinement,  we  have  no  right  to  expect  that 
the  first  crosses  between  them  and  the  canary,  or  that 
their  hybrids,  should  be  perfectly  fertile.  Again,  with 
respect  to  the  fertility  in  successive  generations  of  the 
more  fertile  hybrid  animals,  I  hardly  know  of  an  in- 
stance in  which  two  families  of  the  same  hybrid  have 
been  raised  at  the  same  time  from  different  parents,  so 
as  to  avoid  the  ill  effects  of  close  interbreeding.  On  the 
contrary,  brothers  and  sisters  have  usually  been  crossed 
in  each  successive  generation,  in  opposition  to  the  con- 
stantly repeated  admonition  of  every  breeder.  And  in 
this  case,  it  is  not  at  all  surprising  that  the  inherent 
sterility  in  the  hybrids  should  have  gone  on  increas- 
ing. 

Although  I  know  of  hardly  any  thoroughly  well- 
authenticated  cases  of  perfectly  fertile  hybrid  animals,  I 
have  reason  to  believe  that  the  hybrids  from  Cervulus 
vaginalis  and  Reevesii,  and  from  Phasianus  colchicus 
with  P.  torquatus,  are  perfectly  fertile.  M.  Quatrefages 
states  that  the  hybrids  from  two  moths  (Bombyx  cyn- 
thia  and  arrindia)  were  proved  in  Paris  to  be  fertile  inter 
se  for  eight  generations.  It  has  lately  been  asserted 
that  two  such  distinct  specieg  as  the  hare  and  rabbit, 
when  they  can  be  got  to  breed  together,  produce  off- 
spring, which  are  highly  fertile  when  crossed  with  one 
of  the  parent-species.  The  hybrids  from  the  common 
and  Chinese  geese  (A.  cygnoides),  species  which  are 
so  different  that  they  are  generally  ranked  in  distinct 
genera,  have  often  bred  in  this  country  with  either  pure 
parent,  and  in  one  single  instance  they  have  bred  inter 
27 


10  HYBRIDISM.  [CHAP.  IX. 

se.  This  was  effected  by  Mr.  Eyton,  who  raised  two 
hybrids  from  the  same  parents,  but  from  different 
hatches;  and  from  these  two  birds  he  raised  no  less  than 
eight  hybrids  (grandchildren  of  the  pure  geese)  from  one 
nest.  In  India,  however,  these  cross-bred  geese  must 
be  far  more  fertile;  for  I  am  assured  by  two  eminently 
capable  judges,  namely  Mr.  Blyth  and  Capt.  Hutton, 
that  whole  flocks  of  these  crossed  geese  are  kept  in 
various  parts  of  the  country;  and  as  they  are  kept  for 
profit,  where  neither  pure  parent-species,  exists,  they 
must  certainly  be  highly  or  perfectly  fertile. 

With  our  domesticated  animals,  the  various  races 
when  crossed  together  are  quite  fertile;  yet  in  many 
cases  they  are  descended  from  two  or  more  wild  species. 
From  this  fact  we  must  conclude  either  that  the  abo- 
riginal parent-species  at  first  produced  perfectly  fertile 
hybrids,  or  that  the  hybrids  subsequently  reared  under 
domestication  became  quite  fertile.  .This  latter  alter- 
native, which  was  first  propounded  by  Pallas,  seems  by 
far  the  most  probable,  and  can,  indeed,  hardly  be 
doubted.  It  is,  for  instance,  almost  certain  that  our 
dogs  are  descended  from  several  wild  stocks;  yet,  with 
perhaps  the  exception  of  certain  indigenous  domestic 
dogs  of  South  America,  all  are  quite  fertile  together; 
but  analogy  makes  me  greatly  doubt,  whether  the  sev- 
eral aboriginal  species  would  at  first  have  freely  bred 
together  and  have  produced  quite  fertile  hybrids.  So 
again  I  have  lately  acquired  decisive  evidence  that  the 
crossed  offspring  from  the  Indian  humped  and  common 
cattle  are  inter  se  perfectly  fertile;  and  from  the  ob- 
servations by  Riitimeyer  on  their  important  osteological 
differences,  as  well  as  from  those  by  Mr.  Blyth  on  their 
differences  in  habits,  voice,  constitution,  &c.,  these  two 


CHAP.  IX.]  DEGREES  OP  STERILITY.  H 

forms  must  be  regarded  as  good  and  distinct  species. 
The  same  remarks  may  be  extended  to  the  two  chief 
races  of  the  pig.  We  must,  therefore,  either  give  up 
the  belief  of  the  universal  sterility  of  species  when 
crossed;  or  we  must  look  at  this  sterility  in  animals,  not 
as  an  indelible  characteristic,  but  as  one  capable  of  being 
removed  by  domestication. 

Finally,  considering  all  the  ascertained  facts  on  the 
intercrossing  of  plants  and  animals,  it  may  be  concluded 
that  some  degree  of  sterility,  both  in  first  crosses  and 
in  hybrids,  is  an  extremely  general  result;  but  that  it 
cannot,  under  our  present  state  of  knowledge,  be  con- 
sidered as  absolutely  universal. 

Laws  governing   the   Sterility   of  first   Crosses   and   of 
Hybrids. 

We  will  now  consider  a  little  more  in  detail  the  laws 
governing  the  sterility  of  first  crosses  and  of  hybrids. 
Our  chief  object  will  be  to  see  whether  or  not  these 
laws  indicate  that  species  have  been  specially  endowed 
with  this  quality,  in  order  to  prevent  their  crossing  and 
blending  together  in  utter  confusion.  The  following 
conclusions  are  drawn  up  chiefly  from  Gartner's  ad- 
mirable work  on  the  hybridisation  of  plants.  I  have 
taken  much  pains  to  ascertain  how  far  they  apply  to 
animals,  and,  considering  how  scanty  our  knowledge  is 
in  regard  to  hybrid  animals,  I  have  been  surprised  to 
find  how  generally  the  same  rules  apply  to  both  king- 
doms. 

It  has  been  already  remarked,  that  the  degree  of 
fertility,  both  of  first  crosses  and  of  hybrids,  graduates 
from  zero  to  perfect  fertility.  It  is  surprising  in  how 


12  LAWS  GOVERNING  THE  STERILITY  [CHAP.  IX. 

many  curious  ways  this  gradation  can  be  shown;  but 
only  the  barest  outline  of  the  facts  can  here  be  given. 
When  pollen  from  a  plant  of  one  family  is  placed  on 
the  stigma  of  a  plant  of  a  distinct  family,  it  exerts  no 
more  influence  than  so  much  inorganic  dust.  From 
this  absolute  zero  of  fertility,  the  pollen  of  different  spe- 
cies applied  to  the  stigma  of  some  one  species  of  the 
same  genus,  yields  a  perfect  gradation  in  the  number 
of  seeds  produced,  up  to  nearly  complete  or  even  quite 
complete  fertility;  and,  as  we  have  seen,  in  certain 
abnormal  cases,  even  to  an  excess  of  fertility,  beyond 
that  which  the  plant's  own  pollen  produces.  So  in 
hybrids  themselves,  there  are  some  which  never  have 
produced,  and  probably  never  would  produce,  even 
with  the  pollen  of  the  pure  parents,  a  single  fertile  seed: 
but  in  some  of  these  cases  a  first  trace  of  fertility  may  be 
detected,  by  the  pollen  of  one  of  the  pure  parent-species 
causing  the  flower  of  the  hybrid  to  wither  earlier 
than  it  otherwise  would  have  done;  and  the  early  with- 
ering of  the  flower  is  well  known  to  be  a  sign  of  in- 
cipient 'fertilisation.  From  this  extreme  degree  of 
sterility  we  have  self-fertilised  hybrids  producing  a 
greater  and  greater  number  of  seeds  up  to  perfect  fer- 
tility. 

The  hybrids  raised  from  two  species  which  are  very 
difficult  to  cross,  and  which  rarely  produce  any  off- 
spring, are  generally  very  sterile;  but  the  parallelism 
between  the  difficulty  of  making  a  first  cross,  and  the 
sterility  of  the  hybrids  thus  produced — two  classes  of 
facts  which  are  generally  confounded  together — is  by 
no  means  strict.  There  are  many  cases,  in  which  two 
pure  species,  as  in  the  genus  Verbascum,  can  be  united 
with  unusual  facility,  and  produce  numerous  hybrid- 


CHAP.  IX.]  OF  FIRST  CROSSES  AND  OF  HYBRIDS.         13 

offspring,  yet  these  hybrids  are  remarkably  sterile.  On 
the  other  hand,  there  are  species  which  'can  be  crossed 
very  rarely,  or  with  extreme  difficulty,  but  the  hybrids, 
when  at  last  produced,  are  very  fertile.  Even  within 
the  limits  of  the  same  genus,  for  instance  in  Dianthus, 
these  two  opposite  cases  occur. 

The  fertility,  both  of  first  crosses  and  of  hybrids,  is 
more  easily  affected  by  unfavourable  conditions,  than 
is  that  of  pure  species.  But  the  fertility  of  first  crosses 
is  likewise  innately  variable;  for  it  is  not  always  the 
same  in  degree  when  the  same  two  species  are  crossed 
under  the  same  circumstances;  it  depends  in  part  upon 
the  constitution  of  the  individuals  which  happen  to  have 
been  chosen  for  the  experiment.  So  it  is  with  hybrids, 
for  their  degree  of  fertility  is  often  found  to  differ 
greatly  in  the  several  individuals  raised  from  seed  out 
of  the  same  capsule  and  exposed  to  the  same  condi- 
tions. 

By  flie  term  systematic  affinity  is  meant,  the  general 
resemblance  between  species  in  structure  and  constitu- 
tion. Now  the  fertility  of  first  crosses,  and  of  the 
hybrids  produced  from  them,  is  largely  governed  by 
their  systematic  affinity.  This  is  clearly  shown  by  hy- 
brids never  having  been  raised  between  species  ranked 
by  systematists  in  distinct  families;  and  on  the  other 
hand,  by  very  closely  allied  species  generally  uniting 
with  facility.  But  the  correspondence  between  syste- 
matic affinity  and  the  facility  of  crossing  is  by  no  means 
strict.  A  multitude  of  cases  could  be  given  of  very 
closely  allied  species  which  will  not  unite,*  or  only  with 
extreme  difficulty;  and  on  the  other  hand  of  very  dis- 
tinct species  which  unite  with  the  utmost  facility.  In 
the  same  family  there  may  be  a  genus,  as  Dianthus,  in 


14  LAWS  GOVERNING  THE  STERILITY  [CHAP.  IX. 

which  very  many  species  can  most  readily  be  crossed; 
and  another  ge*nus,  as  Silene,  in  which  the  most  perse- 
vering efforts  have  failed  to  produce  between  extremely 
close  species  a  single  hybrid.  Even  within  the  limits 
of  the  same  genus,  we  meet  with  this  same  difference; 
for  instance,  the  many  species  of  Nicotiana  have  been 
more  largely  crossed  than  the  species  of  almost  any  other 
genus;  but  Gartner  found  that  N.  acuminata,  which 
is  not  a  particularly  distinct  species,  obstinately  failed 
to  fertilise,  or  to  be  fertilised  by  no  less  than  eight  other 
species  of  Nicotiana.  Many  analogous  facts  could  be 
given. 

No  one  has  been  able  to  point  out  what  kind  or  what 
amount  of  difference,  in  any  recognisable  character,  is 
sufficient  to  prevent  two  species  crossing.  It  can  be 
shown  that  plants  most  widely  different  in  habit  and 
general  appearance,  and  having  strongly  marked  differ- 
ences in  every  part  of  the  flower,  even  in  the  pollen,  in 
the  fruit,  and  in  the  cotyledons,  can  be  crossed.  An- 
nual and  perennial  plants,  deciduous  and  evergreen  trees, 
plants  inhabiting  different  stations  and  fitted  for  ex- 
tremely different  climates,  can  often  be  crossed  with 
ease. 

By  a  reciprocal  cross  between  two  species,  I  mean 
the  case,  for  instance,  of  a  female-ass  being  first  crossed 
by  a  stallion,  and  then  a  mare  by  a  male-ass;  these  two 
species  may  then  be  said  to  have  been  reciprocally 
crossed.  There  is  often  the  widest  possible  difference 
in  the  facility  of  making  reciprocal  crosses.  Such  cases 
are  highly  important,  for  they  prove  that  the  capacity 
in  any  two  species  to  cross  is  often  completely  independ- 
ent of  their  systematic  affinity,  that  is  of  any  differ- 
ence in  their  structure  or  constitution,  excepting  in 


CHAP.  IX.]  OP  FIRST  CROSSES  AND  OF  HYBRIDS.         15 

their  reproductive  systems.  The  diversity  of  the  result 
in  reciprocal  crosses  between  the  same  two  species  was 
long  ago  observed  by  Kb'lreuter.  To  give  an  instance: 
Mirabilis  jalapa  can  easily  be  fertilised  by  the  pollen  of 
M.  longiflora,  and  the  hybrids  thus  produced  are  suffi- 
ciently fertile;  but  Kolreuter  tried  more  than  two  hun- 
dred times,  during  eight  following  years,  to  fertilise 
reciprocally  M.  longifiora  with  the  pollen  of  M.  jalapa, 
and  utterly  failed.  Several  other  equally  striking  cases 
could  be  given.  Thuret  has  observed  the  same  fact 
with  certain  sea-weeds  or  Fuci.  Gartner,  moreover, 
found  that  this  difference  of  facility,  in  making  recipro- 
cal crosses  is  extremely  common  in  a  lesser  degree.  He 
has  observed  it  even  between  closely  related  forms  (as 
Matthiola  annua  and  gilabra)  which  many  botanists 
rank  only  as  varieties.  It  is  also  a  remarkable  fact,  that 
hybrids  raised  from  reciprocal  crosses,  though  of  course 
compounded  of  the  very  same  two  species,  the  one  spe- 
cies having  first  been  used  as  the  father  and  then  as 
the  mother,  though  -they  rarely  differ  in  external  char- 
acters, yet  generally  differ  in  fertility  in  a  small,  and  oc- 
casionally in  a  high  degree. 

Several  other  singular  rules  could  be  given  from 
Giirtner:  for  instance,  some  species  have  a  remarkable 
power  of  crossing  with  other  species;  other  species  of 
the  same  genus  have  a  remarkable  power  of  impressing 
their  likeness  on  their  hybrid  offspring;  but  these  two 
powers  do  not  at  all  necessarily  go  together.  There  are 
certain  hybrids  which,  instead  of  having,  as  is  usual, 
an  intermediate  character  between  their  two  parents, 
always  closely  resemble  one  of  them;  and  such  hybrids, 
though  externally  so  like  one  of  their  pure  parent- 
species,  are  with  rare  exceptions  extremely  sterile.  So 


16  LAWS  GOVERNING  THE  STERILITY  [CHAP.  IX. 

again  amongst  hybrids  which  are  usually  intermediate 
in  structure  between  their  parents,  exceptional  and 
abnormal  individuals  sometimes  are  born,  which  closely 
resemble  one  of  their  pure  parents;  and  these  hybrids 
are  almost  always  utterly  sterile,  even  when  the  other 
hybrids  raised  from  seed  from  the  same  capsule  have  a 
considerable  degree  of  fertility.  These  facts  show  how 
completely  the  fertility  of  a  hybrid  may  be  independent 
of  its  external  resemblance  to  either  pure  parent. 

Considering  the  several  rules  now  given,  which 
govern  the  fertility  of  first  crosses  and  of  hybrids,  we 
see  that  when  forms,  which  must  be  considered  as  good 
and  distinct  species,  are  united,  their  fertility  graduates 
from  zero  to  perfect  fertility,  or  even  to  fertility  under 
certain  conditions  in  excess;  that  their  fertility,  besides 
being  eminently  susceptible  to  favourable  and  unfa- 
vourable conditions,  is  innately  variable;  that  it  is  by 
no  means  always  the  same  in  degree  in  the  first  cross 
and  in  the  hybrids  produced  from  this  cross;  that  the 
fertility  of  hybrids  is  not  related  to  the  degree  in  which 
they  resemble  in  external  appearance  either  parent;  and 
lastly,  that  the  facility  of  making  a  first  cross  between 
any  two  species  is  not  always  governed  by  their  syste- 
matic affinity  or  degree  of  resemblance  to  each  other. 
This  latter  statement  is  clearly  proved  by  the  differ- 
ence in  the  result  of  reciprocal  crosses  between  the  same 
two  species,  for,  according  as  the  one  species  or  the 
other  is  used  as  the  father  or  the  mother,  there  is  gen- 
erally soine  difference,  and  occasionally  the  widest  pos- 
sible difference,  in  the  facility  of  effecting  an  union. 
The  hybrids,  moreover,  produced  from  reciprocal  crosses 
often  differ  in  fertility. 

Now  do  these  complex  and  singular  rules  indicate 


CHAP.  IX.]  OF  FIRST  CROSSES  AND  OF  HYBRIDS.         17 

that  species  have  been  endowed  with  sterility  simply 
to  prevent  their  becoming  confounded  in  nature?  I 
think  not.  For  why  should  the  sterility  be  so  extremely 
different  in  degree,  when  various  species  are  crossed, 
all  of  which  we  must  suppose  it  would  be  equally  im- 
portant to  keep  from  blending  together?  Why  should 
the  degree  of  sterility  be  innately  variable  in  the  in- 
dividuals of  the  same  species?  Why  should  some  spe- 
cies cross  with  facility,  and  yet  produce  very  sterile 
hybrids;  and  other  species  cross  with  extreme  difficulty, 
and  yet  produce  fairly  fertile  hybrids?  Why  should 
there  often  be  so  great  a  difference  in  the  result  of  a  re- 
ciprocal cross  between  the  same  two  species?  Why, 
it  may  even  be  asked,  has  the  production  of  hybrids 
been  permitted?  To  grant  to  species  the  special  power 
of  producing  hybrids,  and  then  to  stop  their  further 
propagation  by  different  degrees  of  sterility,  not  strictly 
related  to  the  facility  of  the  first  union  between  their 
parents,  seems  a  strange  arrangement. 

The  foregoing  rules  and  facts,  on  the  other  hand, 
appear  to  me  clearly  to  indicate  that  the  sterility  both 
of  first  crosses  and  of  hybrids  is  simply  incidental  or 
dependent  on  unknown  differences  in  their  reproductive 
systems;  the  differences  being  of  so  peculiar  and  lim- 
ited a  nature,  that,  in  reciprocal  crosses  between  the 
same  two  species,  the  male  sexual  element  of  the  one 
will  often  freely  act  on  the  female  sexual  element  of  the 
other,  but  not  in  a  reversed  direction.  It  will  be  ad- 
visable to  explain  a  little  more  fully  by  an  example  what 
I  mean  by  sterility  being  incidental  on  other  differences, 
and  not  a  specially  endowed  quality.  As  the  capacity 
of  one  plant  to  be  grafted  or  budded  on  another  is  un- 
important for  their  welfare  in  a  state  of  nature,  I  pre- 


18  LAWS  GOVERNING  THE  STERILITY  [CHAP.  IX. 

sume  that  no  one  will  suppose  that  this  capacity  is  a 
specially  endowed  quality,  but  will  admit  that  it  is  inci- 
dental on  differences  in  the  laws  of  growth  of  the  two 
plants.  We  can  sometimes  see  the  reason  why  one  tree 
will  not  take  on  another,  from  differences  in  their  rate  of 
growth,  in  the  hardness  of  their  wood,  in  the  period  of 
the  flow  or  nature  of  their  sap,  &c.;  but  in  a  multitude 
of  cases  we  can  assign  no  reason  whatever.  Great  di- 
versity in  the  size  of  two  plants,  one  being  woody  and 
the  other  herbaceous,  one  being  evergreen  and  the  other 
deciduous,  and  adaptation  to  widely  different  climates, 
do  not  always  prevent  the  two  grafting  together.  As  in 
hybridisation,  so  with  grafting,  the  capacity  is  limited  by 
systematic  affinity,  for  no  one  has  been  able  to  graft 
together  trees  belonging  to  quite  distinct  families;  and, 
on  the  other  hand,  closely  allied  species,  and  varieties 
of  the  same  species,  can  usually,  but  not  invariably,  be 
grafted  with  ease.  But  this  capacity,  as  in  hybridisation, 
is  by  no  means  absolutely  governed  by  systematic 
affinity.  Although  many  distinct  genera  within  the 
same  family  have  been  grafted  together,  in  other  cases 
species  of  the  same  genus  will  not  take  on  each  other. 
The  pear  can  be  grafted  far  more  readily  on  the  quince, 
which  is  ranked  as  a  distinct  genus,  than  on  the  ap- 
ple, which  is  a  member  of  the  same  genus.  Even  dif- 
ferent varieties  of  the  pear  take  with  different  de- 
grees of  facility  on  the  quince;  so  do  different  varie- 
ties of  the  apricot  and  peach  on  certain  varieties  of  the 
plum. 

As  Gartner  found  that  there  was  sometimes  an 
innate  difference  in  different  individuals  of  the  same 
two  species  in  crossing;  so  Sageret  believes  this  to  be 
the  case  with  different  individuals  of  the  same  two  spe- 


CHAP.  IX.]  OF  FIRST  CROSSES  AND  OF  HYBRIDS.         19 

cies  in  being  grafted  together.  As  in  reciprocal  crosses, 
the  facility  of  effecting  an  union  is  often  very  far  from 
equal,  so  it  sometimes  is  in  grafting;  the  common  goose- 
berry, for  instance,  cannot  be  grafted  on  the  current, 
whereas  the  current  will  take,  though  with  difficulty,  on 
the  gooseberry. 

We  have  seen  that  the  sterility  of  hybrids,  which 
have  their  reproductive  organs  in  an  imperfect  con- 
dition, is  a  different  case  from  the  difficulty  of  uniting 
two  pure  species,  which  have  their  reproductive  organs 
perfect;  yet  these  two  distinct  classes  of  cases  run  to 
a  large  extent  parallel.  Something  analogous  occurs 
in  grafting;  for  Thouin  found  that  three  species  of 
Robinia,  which  seeded  freely  on  their  own  roots,  and 
which  could  be  grafted  with  no  great  difficulty  on  a 
fourth  species,  when  thus  grafted  were  rendered  barren. 
On  the  other  hand,  certain  species  of  Sorbus,  when 
grafted  on  other  species  yielded  twice  as  much  fruit  as 
when  on  their  own  roots.  We  are  reminded  by  this 
latter  fact  of  the  extraordinary  cases  of  Hippeastrum, 
Passiflora,  &c.,  which  seed  much  more  freely  when  fertil- 
ised with  the  pollen  of  a  distinct  species,  than  when 
fertilised  with  pollen  from  the  same  plant. 

We  thus  see,  that,  although  there  is  a  clear  and  great 
difference  between  the  mere  adhesion  of  grafted  stocks, 
and  the  union  of  the  male  and  female  elements  in  the 
act  of  reproduction,  yet  that  there  is  a  rude  degree  of 
parallelism  in  the  results  of  grafting  and  of  crossing  dis- 
tinct species.  And  as  we  must  look  at  the  curious  and 
complex  laws  governing  the  facility  with  which  trees  can 
be  grafted  on  each  other  as  incidental  on  unknown  differ- 
ences in  their  vegetative  systems,  so  I  believe  that  the 
still  more  complex  laws  governing  the  facility  of  first 


20  CAUSES  OP  THE  STERILITY        [CHAP.  IX. 

crosses  are  incidental  on  unknown  differences  in  their 
reproductive  systems.  These  differences  in  both  cases, 
follow  to  a  certain  extent,  as  might  have  been  expected, 
systematic  affinity,  by  which  term  every  kind  of  resem- 
blance and  dissimilarity  between  organic  beings  is  at- 
tempted to  be  expressed.  The  facts  by  no  means  seem 
to  indicate  that  the  greater  or  lesser  difficulty  of  either 
grafting  or  crossing  various  species  has  been  a  special 
endowment;  although  in  the  case  of  crossing,  the  diffi- 
culty is  as  important  for  the  endurance  and  stability  of 
specific  forms,  as  in  the  case  of  grafting  it  is  unimpor- 
tant for  their  welfare. 

Origin  and  Causes  of  the  Sterility  of  first  Crosses 
and  of  Hybrids. 

At  one  time  it  appeared  to  me  probable,  as  it  has  to 
others,  that  the  sterility  of  first  crosses  and  of  hybrids 
might  have  been  slowly  acquired  through  the  natural 
selection  of  slightly  lessened  degrees  of  fertility,  which, 
like  any  other  variation,  spontaneously  appeared  in  cer- 
tain individuals  of  one  variety  when  crossed  with  those 
of  another  variety.  For  it  would  clearly  be  advantage- 
ous to  two  varieties  or  incipient  species,  if  they  could  be 
kept  from  blending,  on  the  same  principle  that,  when 
man  is  selecting  at  the  same  time  two  varieties,  it  is 
necessary  that  he  should  keep  them  separate.  In  the 
first  place,  it  may  be  remarked  that  species  inhabiting 
distinct  regions  are  often  sterile  when  crossed;  now  it 
could  clearly  have  been  of  no  advantage  to  such  sepa- 
rated species  to  have  been  rendered  mutually  sterile, 
and  consequently  this  could  not  have  been  effected 
through  natural  selection;  but  it  may  perhaps  be  argued, 


CHAP.  IX.]  OF  FIRST  CROSSES  AND  OF  HYBRIDS.         21 

that,  if  a  species  was  rendered  sterile  with  some  one  com- 
patriot, sterility  with  other  species  would  follow  as  a 
necessary  contingency.  In  the  second  place,  it  is  almost 
as  much  opposed  to  the  theory  of  natural  selection  as  to 
that  of  special  creation,  that  in  reciprocal  crosses  the 
male  element  of  one  form  should  have  been  rendered 
utterly  impotent  on  a  second  form,  whilst  at  the  same 
time  the  male  element  of  this  second  form  is  enabled 
freely  to  fertilise  the  first  form;  for  this  peculiar  state 
of  the  reproductive  system  could  hardly  have  been  ad- 
vantageous to  either  species. 

In  considering  the  probability  of  natural  selection 
having  come  into  action,  in  rendering  species  mutually 
sterile,  the  greatest  difficulty  will  be  found  to  lie  in  the 
existence  of  many  graduated  steps  from  slightly  lessened 
fertility  to  absolute  sterility.  It  may  be  admitted  that 
it  would  profit  an  incipient  species,  if  it  were  rendered 
in  some  slight  degree  sterile  when  crossed  with  its 
parent  form  or  with  some  other  variety;  for  thus  fewer 
bastardised  and  deteriorated  offspring  would  be  pro- 
duced to  commingle  their  blood  with  the  new  species  in 
process  of  formation.  But  he  who  will  take  the  trouble 
to  reflect  on  the  steps  by  which  this  first  degree  of 
sterility  could  be  increased  through  natural  selection 
to  that  high  degree  which  is  common  with  so  many 
species,  and  which  is  universal  with  species  which  have 
been  differentiated  to  a  generic  or  family  rank,  will 
find  the  subject  extraordinarily  complex.  After  mature 
reflection  it  seems  to  me  that  this  could  not  have  been 
effected  through  natural  selection.  Take  the  case  of 
any  two  species  which,  when  crossed,  produced  few  and 
sterile  offspring;  now,  what  is  there  which  could  favour 
the  survival  of  those  individuals  which  happened  to 


22  CAUSES  OF  THE  STERILITY         [CHAP.  IX. 

be  endowed  in  a  slightly  higher  degree  with  mutual 
infertility,  and  which  thus  approached  by  one  small 
step  towards  absolute  sterility?  Yet  an  advance  of 
this  kind,  if  the  theory  of  natural  selection  be  brought  to 
bear,  must  have  incessantly  occurred  with  many  species, 
for  a  multitude  are  mutually  quite  barren.  With  sterile 
neuter  insects  we  have  reason  to  believe  that  modifica- 
tions in  their  structure  and  fertility  have  been  slowly 
accumulated  by  natural  selection,  from  an  advantage 
having  been  thus  indirectly  given  to  the  community  to 
which  they  belonged  over  other  communities  of  the  same 
species;  but  an  individual  animal  not  belonging  to  a  so- 
cial community,  if  rendered  slightly  sterile  when  crossed 
with  some  other  variety,  would  not  thus  itself  gain  any 
advantage  or  indirectly  give  any  advantage  to  the  other 
individuals  of  the  same  variety,  thus  leading  to  their 
preservation. 

But  it  would  be  superfluous  to  discuss  this  question 
in  detail;  for  with  plants  we  have  conclusive  evidence 
that  the  sterility  of  crossed  species  must  be  due  to  some 
principle,  quite  independent  of  natural  selection.  Both 
Gartner  and  Kolreuter  have  proved  that  in  genera  in- 
cluding numerous  species,  a  series  can  be  formed  from 
species  which  when  crossed  yield  fewer  and  fewer  seeds, 
to  species  which  never  produce  a  single  seed,  but  yet 
are  affected  by  the  pollen  of  certain  other  species,  for 
the  germen  swells.  It  is  here  manifestly  impossible  to 
select  the  more  sterile  individuals,  which  have  already 
ceased  to  yield  seeds;  so  that  this  acme  of  sterility, 
when  the  germen  alone  is  affected,  cannot  have  been 
gained  through  selection;  and  from  the  laws  governing 
the  various  grades  of  sterility  being  so  uniform  through- 
out the  animal  and  vegetable  kingdoms,  we  may  infer 


CHAP.  IX.]  OF  FIRST  CROSSES  AND  OF  HYBRIDS.         23 

that  the  cause,  whatever  it  may  be,  is  the  same  or  nearly 
the  same  in  all  cases. 

"We  will  now  look  a  little  closer  at  the  probable  na- 
ture of  the  differences  between  species  which  induce 
sterility  in  first  crosses  and  in  hybrids.  In  the  case  of 
first  crosses,  the  greater  or  less  difficulty  in  effecting  an 
union  and  in  obtaining  offspring  apparently  depends  on 
several  distinct  causes.  There  must  sometimes  be  a 
physical  impossibility  in  the  male  element  reaching  the 
ovule,  as  would  be  the  case  with  a  plant  having  a  pistil 
too  long  for  the  pollen-tubes  to  reach  the  ovarium.  It 
has  also  been  observed  that  when  the  pollen  of  one  spe- 
cies is  placed  on  the  stigma  of  a  distantly  allied  species, 
though  the  pollen-tubes  protrude,  they  do  not  penetrate 
the  stigmatic  surface.  Again,  the  male  element  may 
reach  the  female  element  but  be  incapable  of  causing 
an  embryo  to  be  developed,  as  seems  to  have  been  the 
case  with  some  of  Thuret's  experiments  on  Fuci.  No 
explanation  can  be  given  of  these  facts,  any  more  than 
why  certain  trees  cannot  be  grafted  on  others.  Lastly, 
an  embryo  may  be  developed,  and  then  perish  at  an  early 
period.  This  latter  alternative  has  not  been  sufficiently 
attended  to;  but  I  believe,  from  observations  communi- 
cated to  me  by  Mr.  Hewitt,  who  has  had  great  experience 
in  hybridising  pheasants  and  fowls,  that  the  early  death 
of  the  embryo  is  a  very  frequent  cause  of  sterility  in 
first  crosses.  Mr.  Salter  has  recently  given  the  results 
of  an  examination  of  about  500  eggs  produced  from 
various  crosses  between  three  species  of  Gallus  and  their 
hybrids;  the  majority  of  these  eggs  had  been  fertilised; 
and  in  the  majority  of  the  fertilised  eggs,  the  embryos 
had  either  been  partially  developed  and  had  then  per- 


24  CAUSES  OP  THE  STERILITY        [CHAP.  IX. 

ished,  or  had  become  nearly  mature,  but  the  young 
chickens  had  been  unable  to  break  through  the  shell. 
Of  the  chickens  which  were  born,  more  than  four-fifths 
died  within  the  first  few  days,  or  at  latest  weeks,  "  with- 
out any  obvious  cause,  apparently  from  mere  inability 
to  liv.e; "  so  that  from  the  500  eggs  only  twelve  chick- 
ens were  reared.  With  plants,  hybridised  embryos  prob- 
ably often  perish  in  a  like  manner;  at  least  it  is  known 
that  hybrids  raised  from  very  distinct  species  are  some- 
times weak  and  dwarfed,  and  perish  at  an  early  age; 
of  which  fact  Max  Wichura  has  recently  given  some 
striking  cases  with  hybrid  willows.  It  may  be  here 
worth  noticing  that  in  some  cases  of  parthenogenesis, 
the  embryos  within  the  eggs  of  silk  moths  which  had 
not  been  fertilised,  pass  through  their  early  stages  of 
development  and  then  perish  like  the  embryos  pro- 
duced by  a  cross  between  distinct  species.  Until  becom- 
ing acquainted  with  these  facts,  I  was  unwilling  to  be- 
lieve in  the  frequent  early  death  of  hybrid  embryos;  for 
hybrids,  when  once  born,  are  generally  healthy  and  long- 
lived,  as  we  see  in  the  case  of  the  common  mule.  Hy- 
brids, however,  are  differently  circumstanced  before 
and  after  birth:  when  born  and  living  in  a  country 
where  their  two  parents  live,  they  are  generally  placed 
under  suitable  conditions  of  life.  But  a  hybrid  par- 
takes of  only  half  of  the  nature  and  constitution  of  its 
mother;  it  may  therefore  before  birth,  as  long  as  it  is 
nourished  within  its  mother's  womb,  or  within  the  egg 
or  seed  produced  by  the  mother,  be  exposed  to  condi- 
tions in  some  degree  unsuitable,  and  consequently  be 
liable  to  perish  at  an  early  period;  more  especially  as  all 
very  young  beings  are  eminently  sensitive  to  injurious 
or  unnatural  conditions  of  life.  But  after  all,  the  cause 


CHAP.  IX.]  OF  FIRST  CROSSES  AND  OF  HYBRIDS.         25 

more  probably  lies  in  some  imperfection  in  the  original 
act  of  impregnation,  causing  the  embryo  to  be  imper- 
fectly developed,  rather  than  in  the  conditions  to  which 
it  is  subsequently  exposed. 

In  regard  to  the  sterility  of  hybrids,  in  which  the 
sexual  elements  are  imperfectly  developed,  the  case  is 
somewhat  different.  I  have  more  than  once  alluded  to 
a  large  body  of  facts  showing  that,  when  animals  and 
plants  are  removed  from  their  natural  conditions,  they 
are  extremely  liable  to  have  their  reproductive  systems 
seriously  affected.  This,  in  fact,  is  the  great  bar  to 
the  domestication  of  animals.  Between  the  sterility 
thus  superinduced  and  that  of  hybrids,  there  are  many 
points  of  similarity.  In  both  cases  the  sterility  is  inde- 
pendent of  general  health,  and  is  often  accompanied 
by  excess  of  size  or  great  luxuriance.  In  both  cases  the 
sterility  occurs  in  various  degrees;  in  both,  the  male 
element  is  the  most  liable  to  be  affected;  but  some- 
times the  female  more  than  the  male.  In  both,  the 
tendency  goes  to  a  certain  extent  with  systematic  affin- 
ity, for  whole  groups  of  animals  and  plants  are  rendered 
impotent  by  the  same  unnatural  conditions;  and  whole 
groups  of  species  tend  to  produce  sterile  hybrids.  On 
the  other  hand,  one  species  in  a  group  will  sometimes 
resist  great  changes  of  conditions  with  unimpaired  fer- 
tility; and  certain  species  in  a  group  will  produce  un- 
usually fertile  hybrids.  No  one  can  tell,  till  he  tries, 
whether  any  particular  animal  will  breed  under  confine- 
ment, or  any  exotic  plant  seed  freely  under  culture; 
nor  can  he  tell  till  he  tries,  whether  any  two  species 
of  a  genus  will  produce  more  or  less  sterile  hybrids. 
Lastly,  when  organic  beings  are  placed  during  several 
generations  under  conditions  not  natural  to  them, 


26  CAUSES  OF  THE  STERILITY         [CHAP.  IX. 

they  are  extremely  liable  to  vary,  which  seems  to  be 
partly  due  to  their  reproductive  systems  having  been 
specially  affected,  though  in  a  lesser  degree  than 
when  sterility  ensues.  So  it  is  with  hybrids,  for  their 
offspring  in  successive  generations  are  eminently  liable 
to  vary,  as  every  experimentalist  has  observed. 

Thus  we  see  that  when  organic  beings  are  placed 
under  new  and  unnatural  conditions,  and  when  hybrids 
are  produced  by  the  unnatural  crossing  of  two  species, 
the  reproductive  system,  independently  of  the  general 
state  of  health,  is  affected  in  a  very  similar  manner. 
In  the  one  case,  the  conditions  of  life  have  been  dis- 
turbed, though  often  in  so  slight  a  degree  as  to  be  in- 
appreciable by  us;  in  the  other  case,  or  that  of  hybrids, 
the  external  conditions  have  remained  the  same,  but 
the  organisation  has  been  disturbed  by  two  distinct 
structures  and  constitutions,  including  of  course  the 
reproductive  systems,  having  been  blended  into  one. 
For  it  is  scarcely  possible  that  two  organisations  should 
be  compounded  into  one,  without  some  disturbance 
occurring  in  the  development,  or  periodical  action,  or 
mutual  relations  of  the  different  parts  and  organs  one 
to  another  or  to  the  conditions  of  life.  When  hybrids 
are  able  to  breed  inter  se,  they  transmit  to  their  off- 
spring from  generation  to  generation  the  same  com- 
pounded organisation,  and  hence  we  need  not  be  sur- 
prised that  their  sterility,  though  in  some  degree  varia- 
ble, does  not  diminish;  it  is  even  apt  to  increase,  this 
being  generally  the  result,  as  before  explained,  of  too 
close  interbreeding.  The  above  view  of  the  sterility 
of  hybrids  being  caused  by  two  constitutions  being  com- 
pounded into  one  has  been  strongly  maintained  by  Max 
Wichura. 


CHAP.  IX.]  OF  FIRST  CROSSES  AND  OF  HYBRIDS.         27 

It  must,  however,  be  owned  that  we  cannot  under- 
stand, on  the  above  or  any  other  view,  several  facts 
with  respect  to  the  sterility  of  hybrids;  for  instance, 
the  unequal  fertility  of  hybrids  produced  from  recipro- 
cal crosses;  or  the  increased  sterility  in  those  hybrids 
which  occasionally  and  exceptionally  resemble  closely 
either  pure  parent.  Nor  do  I  pretend  that  the  fore- 
going remarks  go  to  the  root  of  the  matter;  no  explana- 
tion is  offered  why  an  organism,  when  placed  under  un- 
natural conditions,  is  rendered  sterile.  All  that  I  have 
attempted  to  show  is,  that  in  two  cases,  in  some  respects 
allied,  sterility  is  the  common  result, — in  the  one  case 
from  the  conditions  of  life  having  been  disturbed,  in 
the  other  case  from  the  organisation  having  been  dis- 
turbed by  two  organisations  being  compounded  into  one. 

A  similar  parallelism  holds  good  with  an  allied  yet 
very  different  class  of  facts.  It  is  an  old  and  almost 
universal  belief  founded  on  a  considerable  body  of  evi- 
dence, which  I  have  elsewhere  given,  that  slight  changes 
in  the  conditions  of  life  are  beneficial  to  all  living  things. 
We  see  this  acted  on  by  farmers  and  gardeners  in  their 
frequent  exchanges  of  seed,  tubers,  &c.,  from  one  soil 
or  climate  to  another,  and  back  again.  During  the  con- 
valescence of  animals,  great  benefit  is  derived  from  al- 
most any  change  in  their  habits  of  life.  Again,  both 
with  plants  and  animals,  there  is  the  clearest  evidence 
that  a  cross  between  individuals  of  the  same  species, 
which  differ  to  a  certain  extent,  gives  vigour  and  fer- 
tility to  the  offspring;  and  that  close  interbreeding 
continued  during  several  generations  between  the  near- 
est relations,  if  these  be  kept  under  the  same  conditions 
of  life,  almost  always  leads  to  decreased  size,  weakness, 
or  sterility. 


23  STERILITY  OP  HYBRIDS.  [CHAP.  IX. 

Hence  it  seems  that,  on  the  one  hand,  slight 
changes  in  the  conditions  of  life  benefit  all  organic  be- 
ings, and  on  the  other  hand,  that  slight  crosses,  that  is 
crosses  between  the  males  and  females  of  the  same  spe- 
cies, which  have  been  subjected  to  slightly  different 
conditions,  or  which  have  slightly  varied,  give  vigour 
and  fertility  to  the  offspring.  But,  as  we  have  seen,  or- 
ganic beings  long  habituated  to  certain  uniform  condi- 
tions under  a  state  of  nature,  when  subjected,  as  under 
confinement,  to  a  considerable  change  in  their  condi- 
tions, very  frequently  are  rendered  more  or  less  sterile; 
and  we  know  that  a  cross  between  two  forms,  that  have 
become  widely  or  specifically  different,  produce  hybrids 
which  are  almost  always  in  some  degree  sterile.  I  am 
fully  persuaded  that  this  double  parallelism  is  by  no 
means  an  accident  or  an  illusion.  He  who  is  able  to 
explain  why  the  elephant  and  a  multitude  of  other 
animals  are  incapable  of  breeding  when  kept  under  only 
partial  confinement  in  their  native  country,  will  be  able 
to  explain  the  primary  cause  of  hybrids  being  so  gen- 
erally sterile.  He  will  at  the  same  time  be  able  to  ex- 
plain how  it  is  that  the  races  of  some  of  our  domesticated 
animals,  which  have  often  been  subjected  to  new  and 
not  uniform  conditions,  are  quite  fertile  together,  al- 
though they  are  descended  from  distinct  species,  which 
would  probably  have  been  sterile  if  aboriginally  crossed. 
The  above  two  parallel  series  of  facts  seem  to  be  con- 
nected together  by  some  common  but  unknown  bond, 
which  is  essentially  related  to  the  principle  of  life;  this 
principle,  according  to  Mr.  Herbert  Spencer,  being  that 
life  depends  on,  or  consists  in,  the  incessant  action  and 
reaction  of  various  forces,  which,  as  throughout  nature, 
are  always  tending  towards  an  equilibrium;  and  when 


CHAP.  IX.]  DIMORPHISM  AND  TRIMORPHISM.  29 

this  tendency  is  slightly  disturbed  by  any  change,  the 
vital  forces  gain  in  power. 

Reciprocal  Dimorphism  and  Trimorphism. 

This  subject  may  be  here  briefly  discussed,  and  will 
be  found  to  throw  some  light  on  hybridism.  Several 
plants  belonging  to  distinct  orders  present  two  forms, 
which  exist  in  about  equal  numbers  and  which  differ 
in  no  respect  except  in  their  reproductive  organs;  one 
form  having  a  long  pistil  with  short  stamens,  the  other 
a  short  pistil  with  long  stamens;  the  two  having  dif- 
ferently sized  pollen-grains.  With  trimorphic  plants 
there  are  three  forms  likewise  differing  in  the  lengths 
of  their  pistils  and  stamens,  in  the  size  and  colour  of 
the  pollen-grains,  and  in  some  other  respects;  and  as 
in  each  of  the  three  forms  there  are  two  sets  of  stamens, 
the  three  forms  possess  altogether  six  sets  of  stamens 
and  three  kinds  of  pistils.  These  organs  are  so  pro- 
portioned in  length  to  each  other,  that  half  the  sta- 
mens in  two  of  the  forms  stand  on  a  level  with  the 
stigma  of  the  third  form.  Now  I  have  shown,  and  the 
result  has  been  confirmed  by  other  observers,  that, 
in  order  to  obtain  full  fertility  with  these  plants, 
it  is  necessary  that  the  stigma  of  the  one  form  should 
be  fertilised  by  pollen  taken  from  the  stamens  of  cor- 
responding height  in  another  form.  So  that  with  di- 
morphic species  two  unions,  which  may  be  called  legiti- 
mate, are  fully  fertile;  and  two,  which  may  be  called 
illegitimate,  are  more  or  less  infertile.  With  trimor- 
phic species  six  unions  are  legitimate,  or  fully  fer- 
tile,— and  twelve  are  illegitimate,  or  more  or  less  infer- 
tile. 


30  RECIPROCAL  DIMORPHISM  [CHAP.  IX. 

The  infertility  which  may  be  observed  in  various 
dimorphic  and  trimorphic  plants,  when  they  are  il- 
legitimately fertilised,  that  is  by  pollen  taken  from 
stamens  not  corresponding  in  height  with  the  pistil, 
differs  much  in  degree,  up  to  absolute  and  utter  steril- 
ity; just  in  the  same  manner  as  occurs  in  crossing  dis- 
tinct species.  As  the  degree  of  sterility  in  the  latter 
case  depends  in  an  eminent  degree  on  the  conditions 
of  life  being  more  or  less  favourable,  so  I  have  found 
it  with  illegitimate  unions.  It  is  well  known  that  if 
pollen  of  a  distinct  species  be  placed  on  the  stigma  of  a 
flower,  and  its  own  pollen  be  afterwards,  even  after  a 
considerable  interval  of  time,  placed  on  the  same  stigma, 
its  action  is  so  strongly  prepotent  that  it  generally  anni- 
hilates the  effect  of  the»foreign  pollen;  so  it  is  with 
the  pollen  of  the  several  forms  of  the  same  species,  for 
legitimate  pollen  is  strongly  prepotent  over  illegitimate 
pollen,  when  both  are  placed  on  the  same  stigma.  I 
ascertained  this  by  fertilising  several  flowers,  first  il- 
legitimately, and  twenty-four  hours  afterwards  legiti- 
mately with  the  pollen  taken  from  a  peculiarly  coloured 
variety,  and  all  the  seedlings  were  similarly  coloured; 
this  shows  that  the  legitimate  pollen,  though  applied 
twenty-four  hours  subsequently,  had  wholly  destroyed 
or  prevented  the  action  of  the  previously  applied  il- 
legitimate pollen.  Again,  as  in  making  reciprocal 
crosses  between  the  same  two  species,  there  is  occasion- 
ally a  great  difference  in  the  result,  so  the  same  thing 
occurs  with  trimorphic  plants;  for  instance,  the  mid- 
styled  form  of  Lythrum  salicaria  was  illegitimately  fer- 
tilised with  the  greatest  ease  by  pollen  from  the  longer 
stamens  of  the  short-styled  form,  and  yielded  many 
seeds;  but  the  latter  form  did  not  yield  a  single  seed 


CHAP.  IX.]  AND  TRIMORPHISM.  31 

when  fertilised  by  the  longer  stamens  of  the  mid-styled 
form. 

In  all  these  respects,  and  in  others  which  might  be 
added,  the  forms  of  the  same  undoubted  species  when 
illegitimately  united  behave  in  exactly  the  same  manner 
as  do  two  distinct  species  when  crossed.  This  led  me 
carefully  to  observe  during  four  years  many  seedlings, 
raised  from  several  illegitimate  unions.  The  chief  re- 
sult is  that  these  illegitimate  plants,  as  they  may  be 
called,  are  not  fully  fertile.  It  is  possible  to  raise  from 
dimorphic  species,  both  long-styled  and  short-styled 
illegitimate  plants,  and  from  trimorphic  plants  all  three 
illegitimate  forms.  These  can  then  be  properly  united 
in  a  legitimate  manner.  When  this  is  done,  there  is  no 
apparent  reason  why  they  should  not  yield  as  many 
seeds  as  did  their  parents  when  legitimately  fertilised. 
But  such  is  not  the  case.  They  are  all  infertile,  in 
various  degrees;  some  being  so  utterly  and  incurably 
sterile  that  they  did  not  yield  during  four  seasons  a 
single  seed  or  even  seed-capsule.  The  sterility  of  these 
illegitimate  plants,  when  united  with  each  other  in  a 
legitimate  manner,  may  be  strictly  compared  with  that 
of  hybrids  when  crossed  inter  se.  If,  on  the  other  hand, 
a  hybrid  is  crossed  with  either  pure  parent-species,  the 
sterility  is  usually  much  lessened:  and  so  it  is  when 
an  illegitimate  plant  is  fertilised  by  a  legitimate  plant. 
In  the  same  manner  as  the  sterility  of  hybrids  does  not 
always  run  parallel  with  the  difficulty  of  making  the 
first  cross  between  the  two  parent-species,  so  the  sterility 
of  certain  illegitimate  plants  was  unusually  great,  whilst 
the  sterility  of  the  union  from  which  they  were  derived 
was  by  no  means  great.  With  hybrids  raised  from  the 
same  seed-capsule  the  degree  of  sterility  is  innately 


32  RECIPROCAL  DIMORPHISM          [CHAP.  IX. 

variable,  so  it  is  in  a  marked  manner  with  illegitimate 
plants.  Lastly,  many  hybrids  are  profuse  and  persistent 
flowerers,  whilst  other  and  more  sterile  hybrids  pro- 
duce few  flowers,  and  are  weak,  miserable  dwarfs; 
exactly  similar  cases  occur  with  the  illegitimate  off- 
spring of  various  dimorphic  and  trimorphic  plants. 

Altogether  there  is  the  closest  identity  in  character 
and  behaviour  between  illegitimate  plants  and  hybrids. 
It  is  hardly  an  exaggeration  to  maintain  that  illegitimate 
plants  are  hybrids,  produced  within  the  limits  of  the 
same  species  by  the  improper  union  of  certain  forms, 
whilst  ordinary  hybrids  are  produced  from  an  improper 
union  between  so-called  distinct  species.  We  have  also 
already  seen  that  there  is  the  closest  similarity  in  all  re- 
spects between  first  illegitimate  unions  and  first  crosses 
between  distinct  species.  This  will  perhaps  be  made 
more  fully  apparent  by  an  illustration;  we  may  suppose 
that  a  botanist  found  two  well-marked  varieties  (and 
such  occur)  of  the  long-styled  form  of  the  trimorphic 
Lythrum  salicaria,  and  that  he  determined  to  try  by 
crossing  whether  they  were  specifically  distinct.  He 
would  find  that  they  yielded  only  about  one-fifth  of  the 
proper  number  of  seeds,  and  that  they  behaved  in  all 
the  other  above  specified  respects  as  if  they  had  been  two 
distinct  species.  But  to  make  the  case  sure,  he  would 
raise  plants  from  his  supposed  hybridised  seed,  and  he 
would  find  that  the  seedlings  were  miserably  dwarfed 
and  utterly  sterile,  and  that  they  behaved  in  all  other 
respects  like  ordinary  hybrids.  He  might  then  main- 
tain that  he  had  actually  proved,  in  accordance  with 
the  common  view,  that  his  two  varieties  were  as  good 
and  as  distinct  species  as  any  in  the  world;  but  he  would 
be  completely  mistaken. 


CHAP.  IX.]  AND  TRIMORPHISM.  33 

The  facts  now  given  on  dimorphic  and  trimorphic 
plants  are  important,  because  they  show  us,  first,  that 
the  physiological  test  of  lessened  fertility,  both  in  first 
crosses  and  in  hybrids,  is  no  safe  criterion  of  specific 
distinction;  secondly,  because  we  may  conclude  that 
there  is  some  unknown  bond  which  connects  the  in- 
fertility of  illegitimate  unions  with  that  of  their  illegiti- 
mate offspring,  and  we  are  led  to  extend  the  same  view 
to  first  crosses  and  hybrids;  thirdly,  because  we  find, 
and  this  seems  to  me  of  especial  importance,  that  two 
or  three  forms  of  the  same  species  may  exist  and  may 
differ  in  no  respect  whatever,  either  in  structure  or  in 
constitution,  relatively  to  external  conditions,  and  yet 
be  sterile  when  united  in  certain  ways.  For  we  must 
remember  that  it  is  the  union  of  the  sexual  elements  of 
individuals  of  the  same  form,  for  instance,  of  two  long- 
styled  forms,  which  results  in  sterility;  whilst  it  is  the 
union  of  the  sexual  elements  proper  to  two  distinct 
forms  which  is  fertile.  Hence  the  case  appears  at  first 
sight  exactly  the  reverse  of  what  occurs,  in  the  ordinary 
unions  of  the  individuals  of  the  same  species  and  with 
crosses  between  distinct  species.  It  is,  however,  doubt- 
ful whether  this  is  really  so;  but  I  will  not  enlarge  on 
this  obscure  subject. 

We  may,  however,  infer  as  probable  from  the  con- 
sideration of  dimorphic  and  trimorphic  plants,  that  the 
sterility  of  distinct  species  when  crossed  and  of  their 
hybrid  progeny,  depends  exclusively  on  the  nature  of 
their  sexual  elements,  and  not  on  any  difference  in  their 
structure  or  general  constitution.  We  are  also  led  to 
this  same  conclusion  by  considering  reciprocal  crosses, 
in  which  the  male  of  one  species  cannot  be  united,  or 
can  be  united  with  great  difficulty,  with  the  female  of 


34  FERTILITY  OF  VARIETIES          [C HAP.  IX. 

a  second  species,  whilst  the  converse  cross  can  be  effected 
with  perfect  facility.  That  excellent  observer,  Gart- 
ner, likewise  concluded  that  species  when  crossed  are 
sterile  owing  to  differences  confined  to  their  reproduc- 
tive systems. 

Fertility  of  Varieties  when  Crossed,  and  of  their 
Mongrel  Offspring,  not  universal. 

It  may  be  urged,  as  an  overwhelming  argument,  that 
there  must  be  some  essential  distinction  between  species 
and  varieties,  inasmuch  as  the  latter,  however  much 
they  may  differ  from  each  other  in  external  appearance, 
cross  with  perfect  facility,  and  yield  perfectly  fertile 
offspring.  With  some  exceptions,  presently  to  be 
given,  I  fully  admit  that  this  is  the  rule.  But  the  sub- 
ject is  surrounded  by  difficulties,  for,  looking  to  varie- 
ties produced  under  nature,  if  two  forms  hitherto  re- 
puted to  be  varieties  be  found  in  any  degree  sterile  to- 
gether, they  are  at  once  ranked  by  most  naturalists 
as  species.  For  instance,  the  blue  and  red  pimpernel, 
which  are  considered  by  most  botanists  as  varieties,  are 
said  by  Gartner  to  be  quite  sterile  when  crossed,  and 
he  subsequently  ranks  them  as  undoubted  species.  If 
we  thus  argue  in  a  circle,  the  fertility  of  all  varieties 
produced  under  nature  will  assuredly  have  to  be 
granted. 

If  we  turn  to  varieties,  produced,  or  supposed  to  have 
been  produced,  under  domestication,  we  are  still  in- 
volved in  some  doubt.  For  when  it  is  stated,  for  in- 
stance, that  certain  South  American  indigenous  domes- 
tic dogs  do  not  readily  unite  with  European  dogs,  the 
explanation  which  will  occur  to  every  one,  and  probably 


CHAP.  IX.]  WHEN  CROSSED.  35 

the  true  one,  is  that  they  are  descended  from  aborigi- 
nally distinct  species.  Nevertheless  the  perfect  fertil- 
ity of  so  many  domestic  races,  differing  widely  from 
each  other  in  appearance,  for  instance  those  of  the 
pigeon,  or  of  the  cabbage,  is  a  remarkable  fact;  more  es- 
pecially when  we  reflect  how  many  species  there  are, 
which,  though  resembling  each  other  most  closely,  are 
utterly  sterile  when  intercrossed.  Several  considera- 
tions, however,  render  the  fertility  of  domestic  varieties 
less  remarkable.  In  the  first  place,  it  may  be  observed 
that  the  amount  of  external  difference  between  two 
species  is  no  sure  guide  to  their  degree  of  mutual  steril- 
ity, so  that  similar  differences  in  the  case  of  varieties 
would  be  no  sure  guide.  It  is  certain  that  with  species 
the  cause  lies  exclusively  in  differences  in  their  sexual 
constitution.  Now  the  varying  conditions  to  which 
domesticated  animals  and  cultivated  plants  have  been 
subjected,  have  had  so  little  tendency  towards  modify- 
ing the  reproductive  system  in  a  manner  leading  to 
mutual  sterility,  that  we  have  good  grounds  for  admit- 
ting the  directly  opposite  doctrine  of  Pallas,  namely, 
that  such  conditions  generally  eliminate  this  tendency; 
so  that  the  domesticated  descendants  of  species,  which 
in  their  natural  state  probably  would  have  been  in 
some  degree  sterile  when  crossed,  become  perfectly  fer- 
tile together.  With  plants,  so  far  is  cultivation  from 
giving  a  tendency  towards  sterility  between  distinct 
species,  that  in  several  well-authenticated  cases  already 
alluded  to,  certain  plants  have  been  affected  in  an  op- 
posite manner,  for  they  have  become  self-impotent 
whilst  still  retaining  the  capacity  of  fertilising,  and 
being  fertilised  by,  other  species.  If  the  Pallasian  doc- 
trine of  the  elimination  of  sterility  through  long-con- 


36  FERTILITY  OF  VARIETIES          [CHAP.  IX. 

tinued  domestication  be  admitted,  and  it  can  hardly 
be  rejected,  it  becomes  in  the  highest  degree  improbable 
that  similar  conditions  long-continued  should  likewise 
induce  this  tendency;  though  in  certain  cases,  with 
species  having  a  peculiar  constitution,  sterility  might 
occasionally  be  thus  caused.  Thus,  as  I  believe,  we 
can  understand  why  with  domesticated  animals  varieties 
have  not  been  produced  which  are  mutually  sterile;  and 
why  with  plants  only  a  few  such  cases,  immediately  to 
be  given,  have  been  observed. 

The  real  difficulty  in  our  present  subject  is  not,  as  it 
appears  to  me,  why  domestic  varieties  have  not  become 
mutually  infertile  when  crossed,  but  why  this  has  so 
generally  occurred  with  natural  varieties,  as  soon  as  they 
have  been  permanently  modified  in  a  sufficient  degree 
to  take  rank  as  species.  We  are  far  from  precisely 
knowing  the  cause;  nor  is  this  surprising,  seeing  how 
profoundly  ignorant  we  are  in  regard  to  the  normal 
and  abnormal  action  of  the  reproductive  system.  But 
we  can  see  that  species,  owing  to  their  struggle  for  ex- 
istence with  numerous  competitors,  will  have  been  ex- 
posed during  long  periods  of  time  to  more  uniform 
conditions,  than  have  domestic  varieties;  and  this  may 
well  make  a  wide  difference  in  the  result.  For  we 
know  how  commonly  wild  animals  and  plants,  when 
taken  from  their  natural  conditions  and  subjected  to 
captivity,  are  rendered  sterile;  and  the  reproductive 
functions  of  organic  beings  which  have  always  lived 
under  natural  conditions'  would  probably  in  like  man- 
ner be  eminently  sensitive  to  the  influence  of  an  un- 
natural cross.  Domesticated  productions,  on  the  other 
hand,  which,  as  shown  by  the  mere  fact  of  their  domesti- 
cation, were  not  originally  highly  sensitive  to  changes 


CHAP.  IX.]  WHEN  CROSSED.  37 

in  their  conditions  of  life,  and  which  can  now  generally 
resist  with  undiminished  fertility  repeated  changes  of 
conditions,  might  be  expected  to  produce  varieties, 
which  would  be  little  liable  to  have  their  reproductive 
powers  injuriously  affected  by  the  act  of  crossing  with 
other  varieties  which  had  originated  in  a  like  manner. 

I  have  as  yet  spoken  as  if  the  varieties  of  the  same 
species  were  invariably  fertile  when  intercrossed.  But 
it  is  impossible  to  resist  the  evidence  of  the  existence 
of  a  certain  amount  of  sterility  in  the  few  following 
cases,  which  I  will  briefly  abstract.  The  evidence  is 
at  least  as  good  as  that  from  which  we  believe  in  the 
sterility  of  a  multitude  of  species.  The  evidence  is, 
also,  derived  from  hostile  witnesses,  who  in  all  other 
cases  consider  fertility  and  sterility  as  safe  criterions  of 
specific  distinction.  Gartner  kept  during  several  years 
a  dwarf  kind  of  maize  with  yellow  seeds,  and  a  tall 
variety  with  red  seeds  growing  near  each  other  in  his 
garden;  and  although  these  plants  have  separated  sexes, 
they  never  naturally  crossed.  He  then  fertilised  thirteen 
flowers  of  the  one  kind  with  pollen  of  the  other;  but 
only  a  single  head  produced  any  seed,  and  this  one  head 
produced  only  five  grains.  Manipulation  in  this  case 
could  not  have  been  injurious,  as  the  plants  have  sepa- 
rated sexes.  No  one,  I  believe,  has  suspected  that  these 
varieties  of  maize  are  distinct  species;  and  it  is  impor- 
tant to  notice  that  the  bjbrid  plants  thus  raised  were 
themselves  perfectly  fertile;  so  that  even  Gartner  did 
not  venture  to  consider  the  two  varieties  as  specifically 
distinct. 

Girou  de  Buzareingues  crossed  three  varieties  of 
gourd,  which  like  the  maize  has  separated  sexes,  and  he 
asserts  that  their  mutual  fertilisation  is  by  so  much  the 


38  FERTILITY  OF  VARIETIES          [CHAP.  IX. 

less  easy  as  their  differences  are  greater.  How  far  these 
experiments  may  be  trusted,  I  know  not;  but  the  forms 
experimented  on  are  ranked  by  Sageret,  who  mainly 
founds  his  classification  by  the  test  of  infertility,  as 
varieties,  and  Naudin  has  come  to  the  same  conclusion. 

The  following  case  is  far  more  remarkable,  and  seems 
at  first  incredible;  but  it  is  the  result  of  an  astonishing 
number  of  experiments  made  during  many  years  on 
nine  species  of  Verbascum,  by  so  good  an  observer  and 
so  hostile  a  witness  as  Gartner:  namely  that  the  yellow 
and  white  varieties  when  crossed  produce  less  seed  than 
the  similarly  coloured  varieties  of  the  same  species. 
Moreover,  he  asserts  that,  when  yellow  and  white  varie- 
ties of  one  species  are  crossed  with  yellow  and  white 
varieties  of  a  distinct  species,  more  seed  is  produced 
by  the  crosses  between  the  similarly  coloured  flowers, 
than  between  those  which  are  differently  coloured.  Mr. 
Scott  also  has  experimented  on  the  species  and  varieties 
of  Verbascum;  and  although  unable  to  confirm  Gart- 
ner's results  on  the  crossing  of  the  distinct  species,  he 
finds  that  the  dissimilarly  coloured  varieties  of  the 
same  species  yield  fewer  seeds,  in  the  proportion  "of  86 
to  100,  than  the  similarly  coloured  varieties.  Yet  these 
varieties  differ  in  no  respect  except  in  the  colour  of 
their  flowers:  and  one  variety  can  sometimes  be  raised 
from  the  seed  of  another. 

Kolreuter,  whose  accuracy  has  been  confirmed  by 
every  subsequent  observer,  has  proved  the  remarkable 
fact,  that  one  particular  variety  of  the  common  tobacco 
was  more  fertile  than  the  other  varieties,  when  crossed 
with  a  widely  distinct  species.  He  experimented  on 
five  forms  which  are  commonly  reputed  to  be  varieties, 
and  which  he  tested  by  the  severest  trial,  namely,  by 


CHAP.  IX.]  WHEN  CROSSED.  39 

reciprocal  crosses,  and  he  found  their  mongrel  offspring 
perfectly  fertile.  But  one  of  these  five  varieties,  when 
used  either  as  the  father  or  mother,  and  crossed  with 
the  Nicotiana  glutinosa,  always  yielded  hybrids  not  so 
sterile  as  those  which  were  produced  from  the  four 
other  varieties  when  crossed  with  N.  glutinosa.  Hence 
the  reproductive  system  of  this  one  variety  must  have 
been  in  some  manner  and  in  some  degree  modified. 

From  these  facts  it  can  no  longer  be  maintained  that 
varieties  when  crossed  are  invariably  quite  fertile. 
From  the  great  difficulty  of  ascertaining  the  infertility 
of  varieties  in  a  state  of  nature,  for  a  supposed  variety, 
if  proved  to  be  infertile  in  any  degree,  would  almost 
universally  be  ranked  as  a  species; — from  man  attend- 
ing only  to  external  characters  in  his  domestic  varieties, 
and  from  such  varieties  not  having  been  exposed  for 
very  long  periods  to  uniform  conditions  of  life; — from 
these  several  considerations  we  may  conclude  that  fer- 
tility does  not  constitute  a  fundamental  distinction  be- 
tween varieties  and  species  when  crossed.  The  gen- 
eral sterility  of  crossed  species  may  safely  be  looked  at, 
not  as  a  special  acquirement  or  endowment,  but  as  in- 
cidental on  changes  of  an  unknown  nature  in  their  sex- 
ual elements. 


Hybrids  and  Mongrels  compared,  independently  of  their 
fertility. 

Independently  of  the  question  of  fertility,  the  off- 
spring of  species  and  of  varieties  when  crossed  may  be 
compared  in  several  other  respects.  Gartner,  whose 
strong  wish  it  was  to  draw  a  distinct  line  between  spe- 
cies and  varieties,  could  find  very  few,  and,  as  it  seems 


40       HYBRIDS  AND  MONGRELS  COMPARED.    [CHAP.  IX 

to  ine,  quite  unimportant  differences  between  the  so- 
called  hybrid  offspring  of  species,  and  the  so-called 
mongrel  offspring  of  varieties.  And,  on  the  other  hand, 
they  agree  most  closely  in  many  important  respects. 

I  shall  here  discuss  this  subject  with  extreme  brevity. 
The  most  important  distinction  is,  that  in  the  first 
generation  mongrels  are  more  variable  than  hybrids; 
but  Gartner  admits  that  hybrids  from  species  which 
have  long  been  cultivated  are  often  variable  in  the 
first  generation;  and  I  have  myself  seen  striking 
instances  of  this  fact.  Gartner  further  admits  that 
hybrids  between  very  closely  allied  species  are  more 
variable  than  those  from  very  distinct  species;  and 
this  shows  that  the  difference  in  the  degree  of  variabil- 
ity graduates  away.  When  mongrels  and  the  more 
fertile  hybrids  are  propagated  for  several  generations, 
an  extreme  amount  of  variability  in  the  offspring  in 
both  cases  is  notorious;  but  some  few  instances  of  both 
hybrids  and  mongrels  long  retaining  a  uniform  charac- 
ter could  be  given.  The  variability,  however,  in  the 
successive  generations  of  mongrels  is,  perhaps,  greater 
than  in  hybrids. 

This  greater  variability  in  mongrels  than  in  hybrids 
does  not  seem  at  all  surprising.  For  the  parents  of 
mongrels  are  varieties,  and  mostly  domestic  varieties 
(very  few  experiments  having  been  tried  on  natural 
varieties),  and  this  implies  that  there  has  been  recent 
variability,  which  would  often  continue  and  would 
augment  that  arising  from  the  act  of  crossing.  The 
slight  variability  of  hybrids  in  the  first  generation,  in 
contrast  with  that  in  the  succeeding  generations,  is  a 
curious  fact  and  deserves  attention.  For  it  bears  on 
the  view  which  I  have  taken  of  one  of  the  causes  of 


CHAP.  IX.]  HYBRIDS  AND  MONGRELS  COMPARED.        41 

ordinary  variability;  namely,  that  the  reproductive 
system  from  being  eminently  sensitive  to  changed  con- 
ditions of  life,  fails  under  these  circumstances  to  per- 
form its  proper  function  of  producing  offspring  closely 
similar  in  all  respects  to  the  parent-form.  Now  hy- 
brids in  the  first  generation  are  descended  from  spe- 
cies (excluding  those  long-cultivated)  which  have  not 
had  their  reproductive  systems  in  any  way  affected,  and 
they  are  not  variable;  but  hybrids  themselves  have 
their  reproductive  systems  seriously  affected,  and  their 
descendants  are  highly  variable. 

But  to  return  to  our  comparison  of  mongrels  and 
hybrids:  Gartner  states  that  mongrels  are  more  liable 
than  hybrids  to  revert  to  either  parent-form;  but  this, 
if  it  be  true,  is  certainly  only  a  difference  in  degree. 
Moreover,  Gartner  expressly  states  that  hybrids  from 
long  cultivated  plants  are  more  subject  to  reversion 
than  hybrids  from  species  in  their  natural  state;  and 
this  probably  explains  the  singular  difference  in  the 
results  arrived  at  by  different  observers:  thus  Max 
Wichura  doubts  whether  hybrids  ever  revert  to  their 
parent-forms,  and  he  experimented  on  uncultivated 
species  of  willows;  whilst  Naudin,  on  the  other  hand, 
insists  in  the  strongest  terms  on  the  almost  universal 
tendency  to  reversion  in  hybrids,  and  he  experimented 
chiefly  on  cultivated  plants.  Gartner  further  states 
that  when  any  two  species,  although  most  closely  allied 
to  each  other,  are  crossed  with  a  third  species,  the 
hybrids  are  widely  different  from  each  other;  whereas 
if  two  very  distinct  varieties  of  one  species  are  crossed 
with  another  species,  the  hybrids  do  not  differ  much. 
But  this  conclusion,  as  far  as  I  can  make  out,  is 
founded  on  a  single  experiment;  and  seems  directly 


42       HYBRIDS  AND  MONGRELS  COMPARED.  [CHAP.  IX. 

opposed  to  the  results  of  several  experiments  made  by 
Kolreuter. 

Such  alone  are  the  unimportant  differences  which 
Gartner  is  able  to  point  out  between  hybrid  and  mon- 
grel plants.  On  the  other  hand,  the  degrees  and  kinds 
of  resemblance  in  mongrels  and  in  hybrids  to  their 
respective  parents,  more  especially  in  hybrids  pro- 
duced from  nearly  related  species,  follow  according  to 
Gartner  the  same  laws.  When  two  species  are  crossed, 
one  has  sometimes  a  prepotent  power  of  impressing 
its  likeness  on  the  hybrid.  So  I  believe  it  to  be  with 
varieties  of  plants;  and  with  animals  one  variety  cer- 
tainly often  has  this  prepotent  power  over  another 
variety.  Hybrid  plants  produced  from  a  reciprocal  cross, 
generally  resemble  each  other  closely;  and  so  it  is  with 
mongrel  plants  from  a  reciprocal  cross.  Both  hybrids 
and  mongrels  can  be  reduced  to  either  pure  parent- 
form,  by  repeated  crosses  in  successive  generations  with 
either  parent. 

These  several  remarks  are  apparently  applicable  to 
animals;  but  the  subject  is  here  much  complicated, 
partly  owing  to  the  existence  of  secondary  sexual  char- 
acters; but  more  especially  owing  to  prepotency  in 
transmitting  likeness  running  more  strongly  in  one  sex 
than  in  the  other,  both  when  one  species  is  crossed  with 
another,  and  when  one  variety  is  crossed  with  another 
variety.  For  instance,  I  think  those  authors  are  right 
who  maintain  that  the  ass  has  a  prepotent  power  over 
the  horse,  so  that  both  the  mule  and  the  hinny  resemble 
more  closely  the  ass  than  the  horse;  but  that  the  pre- 
potency runs  more  strongly  in  the  male  than  in  the 
female  ass,  so  that  the  mule,  which  is  the  offspring  of 
the  male  ass  and  mare,  is  more  like  an  ass,  than  is 


CHAP.  IX.]     HYBRIDS  AND  MONGRELS  COMPARED.     43 

the  hinny,  which  is  the  offspring  of  the  female  ass  and 
stallion. 

Much  stress  has  been  laid  by  some  authors  on  the 
supposed  fact,  that  it  is  only  with  mongrels  that  the 
offspring  are  not  intermediate  in  character,  but  closely 
resemble  one  of  their  parents;  but  this  does  sometimes 
occur  with  hybrids,  yet  I  grant  much  less  frequently 
than  with  mongrels.  Looking  to  the  cases  which  I 
have  collected  of  cross-bred  animals  closely  resembling 
one  parent,  the  resemblances  seem  chiefly  confined  to 
characters  almost  monstrous  in  their  nature,  and  which 
have  suddenly  appeared — such  as  albinism,  melanism, 
deficiency  of  tail  or  horns,  or  additional  fingers  and 
toes;  and  do  not  relate  to  characters  which  have  been 
slowly  acquired  through  selection.  A  tendency  to  sud- 
den reversions  to  the  perfect  character  of  either  parent 
would,  also,  be  much  more  likely  to  occur  with  mon- 
grels, which  are  descended  from  varieties  often  sud- 
denly produced  and  semi-monstrous  in  character,  than 
with  hybrids,  which  are  descended  from  species  slowly 
and  naturally  produced.  On  the  whole,  I  entirely 
agree  with  Dr.  Prosper  Lucas,  who,  after  arranging  an 
enormous  body  of  facts  with  respect  to  animals,  comes 
to  the  conclusion  that  the  laws  of  resemblance  of  the 
child  to  its  parents  are  the  same,  whether  the  two 
parents  differ  little  or  much  from  each  other,  namely, 
in  the  union  of  individuals  of  the  same  variety,  or  of 
different  varieties,  or  of  distinct  species. 

Independently  of  the  question  of  fertility  and  steril- 
ity, in  all  other  respects  there  seems  to  be  a  general  and 
close  similarity  in  the  offspring  of  crossed  species,  and 
of  crossed  varieties.  If  we  look  at  species  as  having 
been  specially  created,  and  at  varieties  as  having  been 


44  SUMMARY.  [CHAP.  IX. 

produced  by  secondary  laws,  this  similarity  would  be 
an  astonishing  fact.  But  it  harmonises  perfectly  with 
the  view  that  there  is  no  essential  distinction  between 
species  and  varieties. 

Summary  of  Chapter. 

First  crosses  between  forms,  sufficiently  distinct  to 
be  ranked  as  species,  and  their  hybrids,  are  very  gen- 
erally, but  not  universally,  sterile.  The  sterility  is  of 
all  degrees,  and  is  often  so  slight  that  the  most  careful 
experimentalists  have  arrived  at  diametrically  opposite 
conclusions  in  ranking  forms  by  this  test.  The  sterility 
is  innately  variable  in  individuals  of  the  same  spe- 
cies, and  is  eminently  susceptible  to  the  action  of  fa- 
vourable and  unfavourable  conditions.  The  degree  of 
sterility  does  not  strictly  follow  systematic  affinity,  but 
is  governed  by  several  curious  and  complex  laws.  It  is 
generally  different,  and  sometimes  widely  different  in  re- 
ciprocal crosses  between  the  same  two  species.  It  is  not 
always  equal  in  degree  in  a  first  cross  and  in  the  hybrids 
produced  from  this  cross. 

In  the  same  manner  as  in  grafting  trees,  the  capac- 
ity in  one  species  or  variety  to  take  on  another,  is  inci- 
dental on  differences,  generally  of  an  unknown  nature, 
in  their  vegetative,  systems,  so  in  crossing,  the  greater 
or  less  facility  of  one  species  to  unite  with  another  is  in- 
cidental on  unknown  differences  in  their  reproductive 
systems.  There  is  no  more  reason  to  think  that  species 
have  been  specially  endowed  with  various  degrees  of 
sterility  to  prevent  their  crossing  and  blending  in  na- 
ture, than  to  think  that  trees  have  been  specially  en- 
dowed with  various  and  somewhat  analogous  degrees  of 


CHAP.  IX.]  SUMMARY.  45 

difficulty  in  being  grafted  together  in  order  to  prevent 
their  inarching  in  our  forests. 

The  sterility  of  first  crosses  and  of  their  hybrid 
progeny  has  not  been  acquired  through  natural  se- 
lection. In  the  case  of  first  crosses  it  seems  to  depend 
on  several  circumstances;  in  some  instances  in  chief 
part  on  the  early  death  of  the  embryo.  In  the  case  of 
hybrids,  it  apparently  depends  on  their  whole  organi- 
sation having  been  disturbed  by  being  compounded 
from  two  distinct  forms;  the  sterility  being  closely 
allied  to  that  which  so  frequently  affects  pure  species, 
when  exposed  to  new  and  unnatural  conditions  of  life. 
He  who  will  explain  these  latter  cases  will  be  able  to 
explain  the  sterility  of  hybrids.  This  view  is  strongly 
supported  by  a  parallelism  of  another  kind:  namely, 
that,  firstly,  slight  changes  in  the  conditions  of  life 
add  to  the  vigour  and  fertility  of  all  organic  beings; 
and  secondly,  that  the  crossing  of  forms,  which  have 
been  exposed  to  slightly  different  conditions  of  life 
or  which  have  varied,  favours  the  size,  vigour,  and  fer- 
tility of  their  offspring.  The  facts  given  on  the  steril- 
ity of  the  illegitimate  unions  of  dimorphic  and  trimor- 
phic  plants  and  of  their  illegitimate  progeny,  perhaps 
render  it  probable  that  some  unknown  bond  in  all  cases 
connects  the  degree  of  fertility  of  first  unions  with  that 
of  their  offspring.  The  consideration  of  these  facts  on 
dimorphism,  as  well  as  of  the  results  of  reciprocal 
crosses,  clearly  leads  to  the  conclusion  that  the  primary 
cause  of  the  sterility  of  crossed  species  is  confined  to 
differences  in  their  sexual  elements.  But  why,  in  the 
case  of  distinct  species,  the  sexual  elements  should 
so  generally  have  become  more  or  less  modified,  leading 
to  their  mutual  infertility,  we  do  not  know;  but  it 


46  SUMMARY.  [CHAP.  IX. 

seems  to  stand  in  some  close  relation  to  species  having 
been  exposed  for  long  periods  of  time  to  nearly  uniform 
conditions  of  life. 

It  is  not  surprising  that  the  difficulty  in  crossing  any 
two  species,  and  the  sterility  of  their  hybrid  offspring, 
should  in  most  cases  correspond,  even  if  due  to  distinct 
causes:  for  both  depend  on  the  amount  of  difference 
between  the  species  which  are  crossed.  Nor  is  it  sur- 
prising that  the  facility  of  effecting  a  first  cross,  and 
the  fertility  of  the  hybrids  thus  produced,  and  the 
capacity  of  being  grafted  together — though  this  latter 
capacity  evidently  depends  on  widely  different  circum- 
stances— should  all  run,  to  a  certain  extent,  parallel 
with  the  systematic  affinity  of  the  forms  subjected  to 
experiment;  for  systematic  affinity  includes  resem- 
blances of  all  kinds. 

First  crosses  between  forms  known  to  be  varieties,  or 
sufficiently  alike  to  be  considered  as  varieties,  and  their 
mongrel  offspring,  are  very  generally,  but  not,  as  is  so 
often  stated,  invariably  fertile.  Nor  is  this  almost 
universal  and  perfect  fertility  surprising,  when  it  is 
remembered  how  liable  we  are  to  argue  in  a  circle  with 
respect  to  varieties  in  a  state  of  nature;  and  when  we 
remember  that  the  greater  number  of  varieties  have 
been  produced  under  domestication  by  the  selection  of 
mere  external  differences,  and  that  they  have  not  been 
long  exposed  to  uniform  conditions  of  life.  It  should 
also  be  especially  kept  in  mind,  that  long-continued 
domestication  tends  to  eliminate  sterility,  and  is  there- 
fore little  likely  to  induce  this  same  quality.  Inde- 
pendently of  the  question  of  fertility,  in  all  other  re- 
spects there  is  the  closest  general  resemblance  between 
hybrids  and  mongrels, — in  their  variability,  in  their 


CHAP.  IX.]  SUMMARY.  47 

power  of  absorbing  each  other  by  repeated  crosses,  and 
in  their  inheritance  of  characters  from  both  parent- 
forms.  Finally,  then,  although  we  are  as  ignorant  of 
the  precise  cause  of  the  sterility  of  first  crosses  and  of 
hybrids  as  we  are  .why  animals  and  plants  removed 
from  their  natural  conditions  become  sterile,  yet  the 
facts  given  in  this  chapter  do  not  seem  to  me  opposed 
to  the  belief  that  species  aboriginally  existed  as  varie- 
ties. 


48  IMPERFECTION  OF  TEE  .  [CHAP.  X. 


CHAPTER   X. 

ON  THE  IMPERFECTION  OF  THE  GEOLOGICAL  RECORD. 

On  the  absence  of  intermediate  varieties  at  the  present  day — On 
the  nature  of  extinct  intermediate  varieties ;  on  their  number — 
On  the  lapse  of  time,  as  inferred  from  the  rate  of"  denudation 
and  of  deposition — On  the  lapse  of  time  as  estimated  by  years 
— On  the  poorness  of  our  palaeontological  collections — On  the 
intermittence  of  geological  formations— On  the  denudation  of 
granitic  areas — On  the  absence  of  intermediate  varieties  in  any 
one  formation — On  the  sudden  appearance  of  groups  of  species 
— On  their  sudden  appearance  in  the  lowest  known  fossiliferous 
strata— Antiquity  of  the  habitable  earth. 

IN  the  sixth  chapter  I  enumerated  the  chief  objec- 
tions which  might  be  justly  urged  against  the  views 
maintained  in  this  volume.  Most  of  them  have  now 
been  discussed.  One,  namely  the  distinctness  of  spe- 
cific forms,  and  their  not  being  blended  together  by  in- 
numerable transitional  links,  is  a  very  obvious  difficulty. 
I  assigned  reasons  why  such  links  do  not  commonly  oc- 
cur at  the  present  day  under  the  circumstances  ap- 
parently most  favourable  for  their  presence,  namely,  on 
an  extensive  and  continuous  area  with  graduated  phys- 
ical conditions.  I  endeavoured  to  show,  that  the  life  of 
each  species  depends  in  a  more  important  manner  on 
the  presence  of  other  already  defined  organic  forms, 
than  on  climate,  and,  therefore,  that  the  really  govern- 
ing conditions  of  life  do  not  graduate  away  quite  insen- 
sibly like  heat  or  moisture.  I  endeavoured,  also,  to 


CHAP.  X.]  GEOLOGICAL  RECORD.  49 

show  that  intermediate  varieties,  from  existing  in  lesser 
numbers  than  the  forms  which  they  connect,  will  gen- 
erally be  beaten  out  and  exterminated  during  the  course 
of  further  modification  and  improvement.  The  main 
cause,  however,  of  innumerable  intermediate  links  not 
now  occurring  everywhere  throughout  nature,  depends 
on  the  very  process  of  natural  selection,  through  which 
new  varieties  continually  take  the  places  of  and  sup- 
plant their  parent-forms.  But  just  in  proportion  as 
this  process  of  extermination  has  acted  on  an  enormous 
scale,  so  must  the  number  of  intermediate  varieties, 
which  have  formerly  existed,  be  truly  enormous.  Why 
then  is  not  every  geological  formation  and  every  stra- 
tum full  of  such  intermediate  links?  Geology  assured- 
ly does  not  reveal  any  such  finely-graduated  organic 
chain;  and  this,  perhaps,  is  the  most  obvious  and  seri- 
ous objection  which  can  be  urged  against  the  theory. 
The  explanation  lies,  as  I  believe,  in  the  extreme  imper- 
fection of  the  geological  record. 

In  the  first  place,  it  should  always  be  borne  in  mind 
what  sort  of  intermediate  forms  must,  on  the  theory, 
have  formerly  existed.  I  have  found  it  difficult,  when 
looking  at  any  two  species,  to  avoid  picturing  to  my- 
self forms  directly  intermediate  between  them.  But 
this  is  a  wholly  false  view;  we  should  always  look  for 
forms  intermediate  between  each  species  and  a  common 
but  unknown  progenitor;  and  the  progenitor  will  gen- 
erally have  differed  in  some  respects  from  all  its  modi- 
fied descendants.  To  give  a  simple  illustration:  the 
fantail  and  pouter  pigeons  are  both  descended  from 
the  rock-pigeon;  if  we  possessed  all  the  intermediate 
varieties  which  have  ever  existed,  we  should  have  an 
extremely  close  series  between  both  and  the  rock- 


50  IMPERFECTION  OF  THE  [CHAP.  X. 

pigeon;  but  we  should  have  no  varieties  directly  in- 
termediate between  the  fantail  and  pouter;  none,  for 
instance,  combining  a  tail  somewhat  expanded  with 
a  crop  somewhat  enlarged,  the  characteristic  features  of 
these  two  breeds.  These  two  breeds,  moreover,  have 
become  so  much  modified,  that,  if  we  had  no  historical 
or  indirect  evidence  regarding  their  origin,  it  would  not 
have  been  possible  to  have  determined,  from  a  mere 
comparison  of  their  structure  with  that  of  the  rock- 
•pigeon,  C.  livia,  whether  they  had  descended  from  this 
species  or  from  some  other  allied  form,  such  as  C.  cenas. 

So,  with  natural  species,  if  we  look  to  forms  very 
distinct,  for  instance  to  the  horse  and  tapir,  we  have 
no  reason  to  suppose  that  links  directly  intermediate 
between  them  ever  existed,  but  between  each  and  an 
unknown  common  parent.  The  common  parent  will 
have  had  in  its  whole  organisation  much  general  re- 
semblance to  the  tapir  and  to  the  horse;  but  in  some 
points  of  structure  may  have  differed  considerably  from 
both,  even  perhaps  more  than  they  differ  from  each 
other.  Hence,  in  all  such  cases,  we  should  be  unable 
to  recognise  the  parent-form  of  any  two  or  more  spe- 
cies, even  if  we  closely  compared  the  structure  of  the 
parent  with  that  of  its  modified  descendants,  unless  at 
the  same  time  we  had  a  nearly  perfect  chain  of  the  in- 
termediate links. 

It  is  just  possible  by  the  theory,  that  one  of  two 
living  forms  might  have  descended  from  the  other;  for 
instance,  a  horse  from  a  tapir;  and  in  this  case  direct 
intermediate  links  will  have  existed  between  them. 
But  such  a  case  would  imply  that  one  form  had  re- 
mained for  a  very  long  period  unaltered,  whilst  its  de- 
scendants had  undergone  a  vast  amount  of  change; 


CHAP.X.]  GEOLOGICAL  RECORD.  51 

and  the  principle  of  competition  between  organism  and 
organism,  between  child  and  parent,  will  render  this  a 
very  rare  event;  for  in  all  cases  the  new  and  improved 
forms  of  life  tend  to  supplant  the  old  and  unimproved 
forms. 

By  the  theory  of  natural  selection  all  living  species 
have  been  connected  with  the  parent-species  of  each 
genus,  by  differences  not  greater  than  we  see  between 
the  natural  and  domestic  varieties  of  the  same  species 
at  the  present  day;  and  these  parent-species,  now  gen- 
erally extinct,  have  in  their  turn  been  similarly  con- 
nected with  more  ancient  forms;  and  so  on  backwards, 
always  converging  to  the  common  ancestor  of  each 
great  class.  So  that  the  number  of  intermediate  and 
transitional  links,  between  all  living  and  extinct  spe- 
cies, must  have  been  inconceivably  great.  But  as- 
suredly, if  this  theory  be  true,  such  have  lived  upon  the 
earth. 

On  the  Lapse  of  Time,  as  inferred  from  the  rate  of 
Deposition  and  extent  of  Denudation. 

Independently  of  our  not  finding  fossil  remains  of 
such  infinitely  numerous  connecting  links,  it  may  be 
objected  that  time  cannot  have  sufficed  for  so  great  an 
amount  of  organic  change,  all  changes  having  been 
effected  slowly.  It  is  hardly  possible  for  me  to  recall 
to  the  reader  who  is  not  a  practical  geologist,  the  facts 
leading  the  mind  feebly  to  comprehend  the  lapse  of 
time.  He  who  can  read  Sir  Charles  Lyell's  grand  work 
on  the  Principles  of  Geology,  which  the  future  his- 
torian will  recognise  as  having  produced  a  revolution  in 
natural  science,  and  yet  does  not  admit  how  vast  have 


5$  THE  LAPSE  OP  TIME.  [CHAP,  X. 

been  the  past  periods  of  time,  may  at  once  close  this 
volume.  Not  that  it  suffices  to  study  the  Principles  of 
Geology,  or  to  read  special  treatises  by  different  ob- 
servers on  separate  formations,  and  to  mark  how  each 
author  attempts  to  give  an  inadequate  idea  of  the  dura- 
tion of  each  formation,  or  even  of  each  stratum.  We  can 
best  gain  some  idea  of  past  time  by  knowing  the 
agencies  at  work,  and  learning  how  deeply  the  surface  of 
the  land  has  been  denuded,  and  how  much  sediment 
has  been  deposited.  As  Lyell  has  well  remarked,  the 
extent  and  thickness  of  our  sedimentary  formations  are 
the  result  and  the  measure  of  the  denudation  which  the 
earth's  crust  has  elsewhere  undergone.  Therefore  a 
man  should  examine  for  himself  the  great  piles  of  super- 
imposed strata,  and  watch  the  rivulets  bringing  down 
mud,  and  the  waves  wearing  away  the  sea-cliffs,  in 
order  to  comprehend  something  about  the  duration  of 
past  time,  the  monuments  of  which  we  see  all  around 
us. 

It  is  good  to  wander  along  the  coast,  when  formed  of 
moderately  hard  rocks,  and  mark  the  process  of  degra- 
dation. The  tides  in  most  cases  reach  the  cliffs  only  for 
a  short  time  twice  a  day,  and  the  waves  eat  into  them 
only  when  they  are  charged  with  sand  or  pebbles; 
for  there  is  good  evidence  that  pure  water  effects  noth- 
ing in  wearing  away  rock.  At  last  the  base  of  the  cliff 
is  undermined,  huge  fragments  fall  down,  and  these, 
remaining  fixed,  have  to  be  worn  away  atom  by  atom, 
until  after  being  reduced  in  size  they  can  be  rolled 
about  by  the  waves,  and  then  they  are  more  quickly 
ground  into  pebbles,  sand,  or  mud.  But  how  often 
do  we  see  along  the  bases  of  retreating  cliffs  rounded 
boulders,  all  thickly  clothed  by  marine  productions, 


CHAP.  X.]  THE  LAPSE  OP  TIME.  53 

showing  how  little  they  are  abraded  and  how  seldom 
they  are  rolled  about!  Moreover,  if  we  follow  for  a  few 
miles  any  line  of  rocky  cliff,  which  is  undergoing  deg- 
radation, we  find  that  it  is  only  here  and  there,  along 
a  short  length  or  round  a  promontory,  that  the  cliffs 
are  at  the  present  time  suffering.  The  appearance  of 
the  surface  and  the  vegetation  show  that  elsewhere 
years  have  elapsed  since  the  waters  washed  their  base. 

We  have,  however,  recently  learnt  from  the  obser- 
vations of  Ramsay,  in  the  van  of  many  excellent  ob- 
servers— of  Jukes,  Geikie,  Croll,  and  others,  that  sub- 
aerial  degradation  is  a  much  more  important  agency  than 
coast-action,  or  the  power  of  the  waves.  The  whole 
surface  of  the  land  is  exposed  to  the  chemical  action 
of  the  air  and  of  the  rain-water  with  its  dissolved  car- 
bonic acid,  and  in  colder  countries  to  frost;  the  disin- 
tegrated matter  is  carried  down  even  gentle  slopes 
during  heavy  rain,  and  to  a  greater  extent  than  might 
be  supposed,  especially  in  arid  districts,  by  the  wind;  it 
is  then  transported  by  the  streams  and  rivers,  which 
when  rapid  deepen  their  channels,  and  triturate  the 
fragments.  On  a  rainy  day,  even  in  a  gently  undulat- 
ing country,  we  see  the  effects  of  subaerial  degradation 
in  the  muddy  rills  which  flow  down  every  slope.  Messrs. 
Ramsay  and  Whitaker  have  shown,  and  the  observation 
is  a  most  striking  one,  that  the  great  lines  of  escarp- 
ment in  the  Wealden  district  and  those  ranging  across 
England,  which  formerly  were  looked  at  as  ancient  sea- 
coasts,  cannot  have  been  thus  formed,  for  each  line 
is  composed  of  one  and  the  same  formation,  whilst  our 
sea-cliffs  are  everywhere  formed  by  the  intersection 
of  various  formations.  This  being  the  case,  we  are 
compelled  to  admit  that  the  escarpments  owe  their 


54.  THE  LAPSE  OF  TIME.  [CHAP.  X* 

origin  in  chief  part  to  the  rocks  of  which  they  are  com- 
posed having  resisted  subaerial  denudation  better  than 
the  surrounding  surface;  this  surface  consequently  has 
been  gradually  lowered,  with  the  lines  of  harder  rock 
left  projecting.  Nothing  impresses  the  mind  with  the 
vast  duration  of  time,  according  to  our  ideas  of  time, 
more  forcibly  than  the  conviction  thus  gained  that  sub- 
aerial  agencies  which  apparently  have  so  little  power, 
and  which  seem  to  work  so  slowly,  have  produced  great 
results. 

When  thus  impressed  with  the  slow  rate  at  which 
the  land  is  worn  away  through  subaerial  and  littoral 
action,  it  is  good,  in  order  to  appreciate  the  past  dura- 
tion of  time,  to  consider,  on  the  one  hand,  the  masses 
of  rock  which  have  been  removed  over  many  extensive 
areas,  and  on  the  other  hand  the  thickness  of  our  sedi- 
mentary formations.  I  remember  having  been  much 
struck  when  viewing  volcanic  islands,  which  have  been 
worn  by  the  waves  and  pared  all  round  into  perpen- 
dicular cliffs  of  one  or  two  thousand  feet  in  height; 
for  the  gentle  slope  of  the  lava-streams,  due  to  their 
formerly  liquid  state,  showed  at  a  glance  how  far  the 
hard,  rocky  beds  had  once  extended  into  the  open  ocean. 
The  same  story  is  told  still  more  plainly  by  faults, — 
those  great  cracks  along  which  the  strata  have  been  up- 
heaved on  one  side,  or  thrown  down  on  the  other,  to 
the  height  or  depth  of  thousands  of  feet;  for  since  the 
crust  cracked,  and  it  makes  no  great  difference  whether 
the  upheaval  was  sudden,  or,  as  most  geologists  now 
believe,  was  slow  and  effected  by  many  starts,  the  sur- 
face of  the  land  has  been  so  completely  planed  down 
that  no  trace  of  these  vast  dislocations  is  externally 
visible.  The  Craven  fault,  for  instance,  extends  for 


CUAP.  X.]  THE  LAPSE  OF  TIME.  55 

upwards  of  30  miles,  and  along  this  line  the  vertical 
displacement  of  the  strata  varies  from  600  to  3000  feet. 
Professor  Eamsay  has  published  an  account  of  a  down- 
throw in  Anglesea  of  2300  feet;  and  he  informs  me 
that  he  fully  believes  that  there  is  one  in  Merioneth- 
shire of  12,000  feet;  yet  in  these  cases  there  is  nothing 
on  the  surface  of  the  land  to  show  such  prodigious 
movements;  the  pile  of  rocks  on  either  side  of  the  crack 
having  been  smoothly  swept  away. 

On  the  other  hand,  in  all  parts  of  the  world  the  piles 
of  sedimentary  strata  are  of  wonderful  thickness.  In 
the  Cordillera  I  estimated  one  mass  of  conglomerate  at 
ten  thousand  feet;  and  although  conglomerates  have 
probably  been  accumulated  at  a  quicker  rate  than  finer 
sediments,  yet  from  being  formed  of  worn  and  rounded 
pebbles,  each  of  which  bears  the  stamp  of  time,  they 
are  good  to  show  how  slowly  the  mass  must  have  been 
heaped  together.  Professor  Ramsay  has  given  me  the 
maximum  thickness,  from  actual  measurement  in  most 
cases,  of  the  successive  formations  in  different  parts  of 
Great  Britain;  and  this  is  the  result: — 

Feet. 

Palaeozoic  strata  (not  including  igneous  beds) 57,154 

Secondary  strata 13,190 

Tertiary  strata 2,240 

— making  altogether  72,584  feet;  that  is,  very  nearly 
thirteen  and  three-quarters  British  miles.  Some  of  the 
formations,  which  are  represented  in  England  by  thin 
beds,  are  thousands  of  feet  in  thickness  on  the  Con- 
tinent. Moreover,  between  each  successive  formation, 
we  have,  in  the  opinion  of  most  geologists,  blank 
periods  of  enormous  length.  So  that  the  lofty  pile  of 
sedimentary  rocks  in  Britain  gives  but  an  inadequate 


56  THE  LAPSE  OF  TIME.  [CHAP.  X 

idea  of  the  time  which  has  elapsed  during  their  accumu- 
lation. The  consideration  of  these  various  facts  im- 
presses the  mind  almost  in  the  same  manner  as  does  the 
vain  endeavour  to  grapple  with  the  idea  of  eternity. 

Nevertheless  this  impression  is  partly  false.  Mr. 
Croll,  in  an  interesting  paper,  remarks  that  we  do  not 
err  "  in  forming  too  great  a  conception  of  the  length  of 
"  geological  periods,"  but  in  estimating  them  by  years. 
When  geologists  look  at  large  and  complicated  phe- 
nomena, and  then  at  the  figures  representing  several 
million  years,  the  two  produce  a  totally  different  effect 
on  the  mind,  and  the  figures  are  at  once  pronounced  too 
small.  In  regard  to  subaerial  denudation,  Mr.  Croll 
shows,  by  calculating  the  known  amount  of  sediment 
annually  brought  down  by  certain  rivers,  relatively  to 
their  areas  of  drainage,  that  1000  feet  of  solid  rock,  as 
it  became  gradually  disintegrated,  would  thus  be  re- 
moved from  the  mean  level  of  the  whole  area  in  the 
course  of  six  million  years.  This  seems  an  astonishing 
result,  and  some  considerations  lead  to  the  suspicion 
that  it  may  be  too  large,  but  even  if  halved  or  quartered 
it  is  still  very  surprising.  Few  of  us,  however,  know 
what  a  million  really  means:  Mr.  Croll  gives  the  fol- 
lowing illustration:  take  a  narrow  strip  of  paper,  83 
feet  4  inches  in  length,  and  stretch  it  along  the  wall  of 
a  large  hall;  then  mark  off  at  one  end  the  tenth  of  an 
inch.  This  tenth  of  an  inch  will  represent  one  hundred 
years,  and  the  entire  strip  a  million  years.  But  let  it 
be  borne  in  mind,  in  relation  to  the  subject  of  this  work, 
what  a  hundred  years  implies,  represented  as  it  is  by  a 
measure  utterly  insignificant  in  a  hall  of  the  above 
dimensions.  Several  eminent  breeders,  during  a  single 
lifetime,  have  so  largely  modified  some  of  the  higher 


CHAP.  X.]  THE  LAPSE  OF  TIME.  5? 

animals  which  propagate  their  kind  much  more  slowly 
than  most  of  the  lower  animals,  that  they  have  formed 
what  well  deserves  to  be  called  a  new  sub-breed.  Few 
men  have  attended  with  due  care  to  any  one  strain  for 
more  than  half  a  century,  so  that  a  hundred  years  repre- 
sents the  work  of  two  breeders  in  succession.  It  is  not 
to  be  supposed  that  species  in  a  state  of  nature  ever 
change  so  quickly  as  domestic  animals  under  the  guid- 
ance of  methodical  selection.  The  comparison  would 
be  in  every  way  fairer  with  the  effects  which  follow 
from  unconscious  selection,  that  is  the  preservation  of 
the  most  useful  or  beautiful  animals,  with  no  intention 
of  modifying  the  breed;  but  by  this  process  of  uncon- 
scious selection,  various  breeds  have  been  sensibly 
changed  in  the  course  of  two  or  three  centuries. 

Species,  however,  probably  change  much  more 
slowly,  and  within  the  same  country  only  a  few  change 
at  the  same  time.  This  slowness  follows  from  all  the 
inhabitants  of  the  same  country  being  already  so  well 
adapted  to  each  other,  that  new  places  in  the  polity  of 
nature  do  not  occur  until  after  long  intervals,  due  to  the 
occurrence  of  physical  changes  of  some  kind,  or  through 
the  immigration  of  new  forms.  Moreover  variations  or 
individual  differences  of  the  right  nature,  by  which 
some  of  the  inhabitants  might  be  better  fitted  to  their 
new  places  under  the  altered  circumstances,  would  not 
always  occur  at  once.  Unfortunately  we  have  no  means 
of  determining,  according  to  the  standard  of  years,  how 
long  a  period  it  takes  to  modify  a  species;  but  to  the 
subject  of  time  we  must  return. 


58  THE  POORNESS  OF  OUR  [CHAP.  X. 

On  the  Poorness  of  Palceontological  Collections. 

Now  let  us  turn  to  our  richest  geological  museums, 
and  what  a  paltry  display  we  behold!  That  our  col- 
lections are  imperfect  is  admitted  by  every  one.  The 
remark  of  that  admirable  paleontologist,  Edward 
Forbes,  should  never  be  forgotten,  namely,  that  very 
many  fossil  species  are  known  and  named  from  single 
and  often  broken  specimens,  or  from  a  few  specimens 
collected  on  some  one  spot.  Only  a  small  portion  of 
the  surface  of  the  earth  has  been  geologically  explored, 
and  no  part  with  sufficient  care,  as  the  important  dis- 
coveries made  every  year  in  Europe  prove.  No  organ- 
ism wholly  soft  can  be  preserved.  Shells  and  bones  de- 
cay and  disappear  when  left  on  the  bottom  of  the  sea, 
where  sediment  is  not  accumulating.  We  probably  take 
a  quite  erroneous  view,  when  we  assume  that  sediment  is 
being  deposited  over  nearly  the  whole  bed  of  the  sea,  at 
a  rate  sufficiently  quick  to  embed  and  preserve  fossil  re- 
mains. Throughout  an  enormously  large  proportion  of 
the  ocean,  the  bright  blue  tint  of  the  water  bespeaks  its 
purity.  The  many  cases  on  record  of  a  formation  con- 
formably covered,  after  an  immense  interval  of  time,  by 
another  and  later  formation,  without  the  underlying 
bed  having  suffered  in  the  interval  any  wear  and  tear, 
seem  explicable  only  on  the  view  of  the  bottom  of  the 
sea  not  rarely  lying  for  ages  in  an  unaltered  condition. 
The  remains  which  do  become  embedded,  if  in  sand  or 
gravel,  will,  when  the  beds  are  upraised,  generally  be 
dissolved  oy  the  percolation  of  rain-water  charged  with 
carbolic  acid.  Some  of  the  many  kinds  of  animals 
which  live  on  the  beach  between  high  and  low  water 
mark  seem  to  be  rarely  preserved.  For  instance,  the 


CHAP.  X.]    PAL^EONTOLOGICAL  COLLECTIONS.  59 

several  species  of  the  Chthamalinas  (a  sub-family  of 
sessile  cirripedes)  coat  the  rocks  all  over  the  world  in 
infinite  numbers:  they  are  all  strictly  littoral,  with  the 
exception  of  a  single  Mediterranean  species,  which  in- 
habits deep  water,  and  this  has  been  found  fossil  in 
Sicily,  whereas  not  one  other  species  has  hitherto  been 
found  in  any  tertiary  formation:  yet  it  is  known  that 
the  genus  Chthamalus  existed  during  the  Chalk  period. 
Lastly,  many  great  deposits  requiring  a  vast  length  of 
time  for  their  accumulation,  are  entirely  destitute  of 
organic  remains,  without  our  being  able  to  assign  any 
reason:  one  of  the  most  striking  instances  is  that  of  the 
Flysch  formation,  which  consists  of  shale  and  sandstone, 
several  thousand,  occasionally  even  six  thousand  feet  in 
thickness,  and  extending  for  at  least  300  miles  from 
Vienna  to  Switzerland;  and  although  this  great  mass 
has  been  most  carefully  searched,  no  fossils,  except  a 
few  vegetable  remains,  have  been  found. 

With  respect  to  the  terrestrial  productions  which 
lived  during  the  Secondary  and  Palaeozoic  periods,  it  is 
superfluous  to  state  that  our  evidence  is  fragmentary  in 
an  extreme  degree.  For  instance,  until  recently  not  a 
land-shell  was  known  belonging  to  either  of  these  vast 
periods,  with  the  exception  of  one  species  discovered  by 
Sir  C.  Lyell  and  Dr.  Dawson  in  the  carboniferous  strata 
of  Xorth  America;  but  now  land-shells  have  been  found 
in  the  lias.  In  regard  to  mammiferous  remains,  a 
glance  at  the  historical  table  published  in  LyelPs 
Manual  will  bring  home  the  truth,  how  accidental  and 
rare  is  their  preservation,  far  better  than  pages  of  detail. 
Nor  is  their  rarity  surprising,  when  we  remember  how 
large  a  proportion  of  the  bones  of  tertiary  mammals 
have  been  discovered  either  in  caves  or  in  lacustrine 


60  THE  POORNESS  OF   OUR  [CHAP.  X. 

deposits;  and  that  not  a  cave  or  true  lacustrine  bed  is 
known  belonging  to  the  age  of  our  secondary  or  palaeo- 
zoic formations. 

But  the  imperfection  in  the  geological  record  largely 
results  from  another  and  more  important  cause  than 
any  of  the  foregoing;  namely,  from  the  several  forma- 
tions being  separated  from  each  other  by  wide  intervals 
of  time.  This  doctrine  has  been  emphatically  admitted 
by  many  geologists  and  palaeontologists,  who,  like  E. 
Forbes,  entirely  disbelieve  in  the  change  of  species. 
When  we  see  the  formations  tabulated  in  written  works, 
or  when  we  follow  them  in  nature,  it  is  difficult  to 
avoid  believing  that  they  are  closely  consecutive.  But 
we  know,  for  instance,  from  Sir  R.  Murchi  son's  great 
work  on  Russia,  what  wide  gaps  there  are  in  that  coun- 
try between  the  superimposed  formations;  so  it  is  in 
North  America,  and  in  many  other  parts  of  the  world. 
The  most  skilful  geologist,  if  his  attention  had  been 
confined  exclusively  to  these  large  territories,  would 
never  have  suspected  that,  during  the  periods  which 
were  blank  and  barren  in  his  own  country,  great  piles 
of  sediment,  charged  with  new  and  peculiar  forms  of 
life,  had  elsewhere  been  accumulated.  And  if,  in  each 
separate  territory,  hardly  any  idea  can  be  formed  of  the 
length  of  time  which  has  elapsed  between  the  consecu- 
tive formations,  we  may  infer  that  this  could  nowhere 
be  ascertained.  The  frequent  and  great  changes  in 
the  mineralogical  composition  of  consecutive  forma- 
tions, generally  implying  great  changes  in  the  geography 
of  the  surrounding  lands,  whence  the  sediment  was 
derived,  accord  with  the  belief  of  vast  intervals  of  time 
having  elapsed  between  each  formation. 

We  can,  I  think,  see  why  the  geological  formations 


CHAP.  X.]  PAL^ONTOLOGICAL  COLLECTIONS.  61 

of  each  region  are  almost  invariably  intermittent;  that 
is,  have  not  followed  each  other  in  close  sequence. 
Scarcely  any  fact  struck  me  more  when  examining 
many  hundred  miles  of  the  South  American  coasts, 
which  have  been  upraised  several  hundred  feet  within 
the  recent  period,  than  the  absence  of  any  recent  de- 
posits sufficiently  extensive  to  last  for  even  a  short 
geological  period.  Along  the  whole  west  coast,  which  is 
inhabited  by  a  peculiar  marine  fauna,  tertiary  beds  are 
so  poorly  developed,  that  no  record  of  several  successive 
and  peculiar  marine  faunas  will  probably  be  preserved 
to  a  distant  age.  A  little  reflection  will  explain  why, 
along  the  rising  coast  of  the  western  side  of  South 
America,  no  extensive  formations  with  recent  or  ter- 
tiary remains  can  anywhere  be  found,  though  the  supply 
of  sediment  must  for  ages  have  been  great,  from  the 
enormous  degradation  of  the  coast-rocks  and  from 
muddy  streams  entering  the  sea.  The  explanation,  no 
doubt,  is,  that  the  littoral  and  sub-littoral  deposits  are 
continually  worn  away,  as  soon  as  they  are  brought  up 
by  the  slow  and  gradual  rising  of  the  land  within  the 
grinding  action  of  the  coast-waves. 

We  may,  I  think,  conclude  that  sediment  must  be 
accumulated  in  extremely  thick,  solid,  or  extensive 
masses,  in  order  to  withstand  the  incessant  action  of 
the  waves,  when  first  upraised  and  during  successive 
oscillations  of  level  as  well  as  the  subsequent  subaerial 
degradation.  Such  thick  and  extensive  accumulations 
of  sediment  may  be  formed  in  two  ways;  either  in  pro- 
found depths  of  the  sea,  in  which  case  the  bottom  will 
not  be  inhabited  by  so  many  and  such  varied  forms  of 
life,  as  the  more  shallow  seas;  and  the  mass  when  up- 
raised will  give  an  imperfect  record  of  the  organisms 


62  THE  POORNESS  OF  OUR  [CHAP.  X. 

which  existed  in  the  neighbourhood  during  the  period 
of  its  accumulation.  Or,  sediment  may  be  deposited  to 
any  thickness  and  extent  over  a  shallow  bottom,  if  it 
continue  slowly  to  subside.  In  this  latter  case,  as  long 
as  the  rate  of  subsidence  and  the  supply  of  sediment 
nearly  balance  each  other,  the  sea  will  remain  shallow 
and  favourable  for  many  and  varied  forms,  and  thus 
a  rich  fossiliferous  formation,  thick  enough,  when  up- 
raised, to  resist  a  large  amount  of  denudation,  may  be 
formed. 

I  am  convinced  that  nearly  all  our  ancient  forma- 
tions, which  are  throughout  the  greater  part  of  their 
thickness  rich  in  fossils,  have  thus  been  formed  during 
subsidence.  Since  publishing  my  views  on  this  subject 
in  1845,  I  have  watched  the  progress  of  Geology,  and 
have  been  surprised  to  note  how  author  after  author, 
in  treating  of  this  or  that  great  formation,  has  come  to 
the  conclusion  that  it  was  accumulated  during  subsi- 
dence. I  may  add,  that  the  only  ancient  tertiary  forma- 
tion on  the  west  coast  of  South  America,  which  has 
been  bulky  enough  to  resist  such  degradation  as  it  has 
as  yet  suffered,  but  which  will  hardly  last  to  a  dis- 
tant geological  age,  was  deposited  during  a  downward 
oscillation  of  level,  and  thus  gained  considerable  thick- 


All  geological  facts  tell  us  plainly  that  each  area 
has  undergone  numerous  slow  oscillations  of  level,  and 
apparently  these  oscillations  have  affected  wide  spaces. 
Consequently,  formations  rich  in  fossils  and  sufficiently 
thick  and  extensive  to  resist  subsequent  degradation, 
will  have  been  formed  over  wide  spaces  during  periods 
of  subsidence,  but  only  where  the  supply  of  sediment 
was  sufficient  to  keep  the  sea  shallow  and  to  embed 


CHAP.  X.]  PAL^IONTOLOGICAL  COLLECTIONS.     „        63 

and  preserve  the  remains  before  they  had  time  to  de- 
cay. On  the  other  hand,  as  long  as  the  bed  of  the  sea 
remains  stationary,  thick  deposits  cannot  have  been  ac- 
cumulated in  the  shallow  parts,  which  are  the  most 
favourable  to  life.  Still  less  can  this  have  happened 
during  the  alternate  periods  of  elevation;  or,  to  speak 
more  accurately,  the  beds  which  were  then  accumu- 
lated will  generally  have  been  destroyed  by  being 
upraised  and  brought  within  the  limits  of  the  coast- 
action. 

These  remarks  apply  chiefly  to  littoral  and  sub-lit- 
toral deposits.  In  the  case  of  an  extensive  and  shallow 
sea,  such  as  that  within  a  large  part  of  the  Malay  Archi- 
pelago, where  the  depth  varies  from  30  or  40  to  60 
fathoms,  a  widely  extended  formation  might  be  formed 
during  a  period  of  elevation,  and  yet  not  suffer  exces- 
sively from  denudation  during  its  slow  upheaval;  but 
the  thickness  of  the  formation  could  not  be  great,  for 
owing  to  the  elevatory  movement  it  would  be  less  than 
the  depth  in  which  it  was  formed;  nor  would  the  de- 
posit be  much  consolidated,  nor  be  capped  by  overlying 
formations,  so  that  it  would  run  a  good  chance  of  being 
worn  away  by  atmospheric  degradation  and  by  the  ac- 
tion of  the  sea  during  subsequent  oscillations  of  level. 
It  has,  however,  been  suggested  by  Mr.  Hopkins,  that 
if  one  part  of  the  area,  after  rising  and  before  being 
denuded,  subsided,  the  deposit  formed  during  the  ris- 
ing movement,  though  not  thick,  might  afterwards  be- 
come protected  by  fresh  accumulations,  and  thus  be 
preserved  for  a  long  period. 

Mr.  Hopkins  also  expresses  his  belief  that  sedimen- 
tary beds  of  considerable  horizontal  extent  have  rarely 
been  completely  destroyed.  But  all  geologists,  except- 


6-t  THE  POORNESS  OF  OUR  [CHAP.  X. 

ing  the  few  who  believe  that  our  present  metamorphic 
schists  and  plutonic  rocks  once  formed  the  primordial 
nucleus  of  the  globe,  will  admit  that  these  latter  rocks 
have  been  stript  of  their  covering  to  an  enormous  ex- 
tent. For  it  is  scarcely  possible  that  such  rocks  could 
have  been  solidified  and  crystallized  whilst  uncovered; 
but  if  the  metamorphic  action  occurred  at  profound 
depths  of  the  ocean,  the  former  protecting  mantle  of 
rock  may  not  have  been  very  thick.  Admitting  then 
that  gneiss,  mica-schist,  granite,  diorite,  &c.,  were 
once  necessarily  covered  up,  how  can  we  account  for 
the  naked  and  extensive  areas  of  such  rocks  in  many 
parts  of  the  world,  except  on  the  belief  that  they  have 
subsequently  been  completely  denuded  of  all  overlying 
strata?  That  such  extensive  areas  do  exist  cannot  be 
doubted:  the  granitic  region  of  Parime  is  described  by 
Humboldt  as  being  at  least  nineteen  times  as  large  as 
Switzerland.  South  of  the  Amazon,  Boue  colours  an 
area  composed  of  rocks  of  this  nature  as  equal  to  that 
of  Spain,  France,  Italy,  part  of  Germany,  and  the 
British  Islands,  all  conjoined.  This  region  has  not 
been  carefully  explored,  but  from  the  concurrent  testi- 
mony of  travellers,  the  granitic  area  is  very  large:  thus, 
Von  Eschwege  gives  a  detailed  section  of  these  rocks, 
stretching  from  Eio  de  Janeiro  for  260  geographical 
miles  inland  in  a  straight  line;  and  I  travelled  for  150 
miles  in  another  direction,  and  saw  nothing  but  granitic 
rocks.  Numerous  specimens,  collected  along  the 
whole  coast  from  near  Rio  Janeiro  to  the  mouth  of  the 
Plata,  a  distance  of  1100  geographical  miles,  were  ex- 
amined by  me,  and  they  all  belonged  to  this  class.  In- 
land, along  the  whole  northern  bank  of  the  Plata  I 
saw,  besides  modern  tertiary  beds,  only  one  small  patch 


CHAP.  X.]  PAL^ONTOLOGICAL  COLLECTIONS.  65> 

of  slightly  metamorphosed  rock,  which  alone  could  have 
formed  a  part  of  the  original  capping  of  the  granitic 
series.  Turning  to  a  well-known  region,  namely,  to 
the  United  States  and  Canada,  as  shown  in  Professor 
H.  D.  Rogers's  beautiful  map,  I  have  estimated  the 
areas  by  cutting  out  and  weighing  the  paper,  and  I 
find  that  the  metamorphic  (excluding  "  the  semi-meta- 
"  morphic  ")  and  granitic  rocks  exceed,  in  the  propor- 
tion of  19  to  12.5,  the  whole  of  the  newer  Paleozoic 
formations.  In  many  regions  the  metamorphic  and 
granitic  rocks  would  be  found  much  more  widely  ex- 
tended than  they  appear  to  be,  if  all  the  sedimentary 
beds  were  removed  which  rest  unconformably  on  them, 
and  which  could  not  have  formed  part  of  the  original 
mantle  under  which  they  were  crystallized.  Hence  it 
is  probable  that  in  some  parts  of  the  world  whole  forma- 
tions have  been  completely  denuded,  with  not  a  wreck 
left  behind. 

One  remark  is  here  worth  a  passing  notice.  During 
periods  of  elevation  the  area  of  the  land  and  of  the  ad- 
joining shoal  parts  of  the  sea  will  be  increased,  and  new 
stations  will  often  be  formed: — all  circumstances  favour- 
able, as  previously  explained,  for  the  formation  of 
new  varieties  and  species;  but  during  such  periods  there 
will  generally  be  a  blank  in  the  geological  record.  On 
the  other  hand,  during  subsidence,  the  inhabited  area 
and  number  of  inhabitants  will  decrease  (excepting  on 
the  shores  of  a  continent  when  first  broken  up  into  an 
archipelago),  and  consequently  during  subsidence, 
though  there  will  be  much  extinction,  few  new  varie- 
ties or  species  will  be  formed;  and  it  is  during  these 
very  periods  of  subsidence,  that  the  deposits  which  are 
richest  in  fossils  have  been  accumulated. 


66    ABSENCE  OF  INTERMEDIATE  VARIETIES  [CnAP.X. 

On  the  Absence  of  Numerous  Intermediate  Varieties  in 
any  Single  Formation. 

From  these  several  considerations,  it  cannot  be 
doubted  that  the  geological  record,  viewed  as  a  whole, 
is  extremely  imperfect;  but  if  we  confine  our  attention 
to  any  one  formation,  it  becomes  much  more  difficult  to 
understand  why  we  do  not  therein  find  closely  gradu- 
ated varieties  between  the  allied  species  which  lived  at 
its  commencement  and  at  its  close.  Several  cases  are 
on  record  of  the  same  species  presenting  varieties  in 
the  upper  and  lower  parts  of  the  same  formation;  thus, 
Trautschold  gives  a  number  of  instances  with  Am- 
monites; and  Hilgendorf  has  described  a  most  curious 
case  of  ten  graduated  forms  of  Planorbis  multiformis  in 
the  successive  beds  of  a  fresh-water  formation  in  Swit- 
zerland. Although  each  formation  has  indisputably 
required  a  vast  number  of  •years  for  its  deposition,  sev- 
eral reasons  can  be  given  why  each  should  not  commonly 
include  a  graduated  series  of  links  between  the  species 
which  lived  at  its  commencement  and  close;  but  I 
cannot  assign  due  proportional  weight  to  the  following 
considerations. 

Although  each  formation  may  mark  a  very  long 
lapse  of  years,  each  probably  is  short  compared  with  the 
period  requisite  to  change  one  species  into  another.  I 
am  aware  that  two  palaeontologists,  whose  opinions  are 
worthy  of  much  deference,  namely  Bronn  and  "Wood- 
ward, have  concluded  that  the  average  duration  of  each 
formation  is  twice  or  thrice  as  long  as  the  average  dura- 
tion of  specific  forms.  But  insuperable  difficulties, 
as  it  seems  to  me,  prevent  us  from  coming  to  any  just 
conclusion  on  this  head.  When  we  see  a  species  first 


CHAP.X.]         IN  ANY  SINGLE  FORMATION.  67 

appearing  in  the  middle  of  any  formation,  it  would  be 
rash  in -the  extreme  to  infer  that  it  had  not  elsewhere 
previously  existed.  So  again  when  we  find  a  species 
disappearing  before  the  last  layers  have  been  deposited, 
it  would  be  equally  rash  to  suppose  that  it  then  became 
extinct.  We  forget  how  small  the  area  of  Europe  is 
compared  with  the  rest  of  the  world;  nor  have  the  sev- 
eral stages  of  the  same  formation  throughout  Europe 
been  correlated  with  perfect  accuracy. 

We  may  safely  infer  that  with  marine  animals  of  all 
kinds  there  has  been  a  large  amount  of  migration  due 
to  climatal  and  other  changes;  and  when  we  see  a 
species  first  appearing  in  any  formation,  the  probabil- 
ity is  that  it  only  then  first  immigrated  into  that  area. 
It  is  well-known,  for  instance,  that  several  species  ap- 
pear somewhat  earlier  in  the  paleozoic  beds  of  North 
America  than  in  those  of  Europe;  time  having  appa- 
rently been  required  for  their  migration  from  the 
American  to  the  European  seas.  In  examining  the 
latest  deposits  in  various  quarters  of  the  world,  it  has 
everywhere  been  noted,  that  some  few  still  existing 
species  are  common  in  the  deposit,  but  have  become 
extinct  in  the  immediately  surrounding  sea;  or,  con- 
versely, that  some  are  now  abundant  in  the  neighbour- 
ing sea,  but  are  rare  or  absent  in  this  particular  deposit. 
It  is  an  excellent  lesson  to  reflect  on  the  ascertained 
amount  of  migration  of  the  inhabitants  of  Europe  dur- 
ing the  glacial  epoch,  which  forms  only  a  part  of  one 
whole  geological  period;  and  likewise  to  reflect  on  the 
changes  of  level,  on  the  extreme  change  of  climate,  and 
on  the  great  lapse  of  time,  all  included  within  this 
same  glacial  period.  Yet  it  may  be  doubted  whether, 
in  any  quarter  of  the  world,  sedimentary  deposits,  in- 


68  ABSENCE  OF  INTERMEDIATE  VARIETIES  [CHAP.  X. 

including  fossil  remains,  have  gone  on  accumulating 
within  the  same  area  during  the  whole  of  this  period. 
It  is  not,  for  instance,  probable  that  sediment  was  de- 
posited during  the  whole  of  the  glacial  period  near 
the  mouth  of  the  Mississippi,  within  that  limit  of  depth 
at  which  marine  animals  can  best  flourish:  for  we  know 
that  great  geographical  changes  occurred  in  other  parts 
of  America  during  this  space  of  time.  When  such 
beds  as  were  deposited  in  shallow  water  near  the  mouth 
of  the  Mississippi  during  some  part  of  the  glacial  period 
shall  have  been  upraised,  organic  remains  will  prob- 
ably first  appear  and  disappear  at  different  levels,  ow- 
ing to  the  migrations  of  species  and  to  geographical 
changes.  And  in  the  distant  future,  a  geologist,  ex- 
amining these  beds,  would  be  tempted  to  conclude  that 
the  average  duration  of  life  of  the  embedded  fossils  had 
been  less  than  that  of  the  glacial  period,  instead  of  hav- 
ing been  really  far  greater,  that  is,  extending  from  be- 
fore the  glacial  epoch  to  the  present  day. 

In  order  to  get  a  perfect  gradation  between  two 
forms  in  the  upper  and  lower  parts  of  the  same  forma- 
tion, the  deposit  must  have  gone  on  continuously  ac- 
cumulating during  a  long  period,  sufficient  for  the  slow 
process  of  modification;  hence  the  deposit  must  be 
a  very  thick  one;  and  the  species  undergoing  change 
must  have  lived  in  the  same  district  throughout  the 
whole  time.  But  we  have  seen  that  a  thick  formation, 
fossiliferous  throughout  its  entire  thickness,  can  ac- 
cumulate only  during  a  period  of  subsidence:  and  to 
keep  the  depth  approximately  the  same,  which  is  neces- 
sary that  the  same  marine  species  may  live  on  the  same 
space,  the  supply  of  sediment  must  nearly  counterbal- 
ance the  amount  of  subsidence.  But  this  same  move- 


CHAP.  X.]         IN  ANY  SINGLE  FORMATION.  69 

ment  of  subsidence  will  tend  to  submerge  the  area 
whence  the  sediment  is  derived,  and  thus  diminish  the 
supply,  whilst  the  downward  movement  continues.  In 
fact,  this  nearly  exact  balancing  between  the  supply  of 
sediment  and  the  amount  of  subsidence  is  probably  a 
rare  contingency;  for  it  has  been  observed  by  more  than 
one  paleontologist,  that  very  thick  deposits  are  usually 
barren  of  organic  remains,  except  near  their  upper  or 
lower  limits. 

It  would  seem  that  each  separate  formation,  like  the 
whole  pile  of  formations  in  any  country,  has  generally 
been  intermittent  in  its  accumulation.  When  we  see, 
as  is  so  often  the  case,  a  formation  composed  of  beds 
of  widely  different  mineralogical  composition,  we  may 
reasonably  suspect  that  the  process  of  deposition  has 
been  more  or  less  interrupted.  Nor  will  the  closest 
inspection  of  a  formation  give  us  any  idea  of  the  length 
of  time  which  its  deposition  may  have  consumed. 
Many  instances  could  be  given  of  beds  only  a  few  feet 
in  thickness,  representing  formations,  which  are  else- 
where thousands  of  feet  in  thickness,  and  which  must 
have  required  an  enormous  period  for  their  accumula- 
tion; yet  no  one  ignorant  of  this  fact  would  have  even 
suspected  the  vast  lapse  of  time  represented  by  the 
thinner  formation.  Many  cases  could  be  given  of  the 
lower  beds  of  a  formation  having  been  upraised,  de- 
nuded, submerged,  and  then  re-covered  by  the  upper 
beds  of  the  same  formation, — facts,  showing  what  wide, 
yet  easily  overlooked,  intervals  have  occurred  in  its  ac- 
cumulation. In  other  cases  we  have  the  plainest  evi- 
dence in  great  fossilised  trees,  still  standing  upright 
as  they  grew,  of  many  long  intervals  of  time  and  changes 
of  level  during  the  process  of  deposition,  which  would 


70  ABSENCE  OF  INTERMEDIATE  VARIETIES  [CHAP.  X. 

not  have  been  suspected,  had  not  the  trees  been  pre- 
served: thus  Sir  C.  Lyell  and  Dr.  Dawson  found  carbon- 
iferous beds  1400  feet  thick  in  Nova  Scotia,  with  an- 
cient root-bearing  strata,  one  above  the  other  at  no 
less  than  sixty-eight  different  levels.  Hence,  when  the 
same  species  occurs  at  the  bottom,  middle,  and  top  of  a 
formation,  the  probability  is  that  it  has  not  lived  on  the 
same  spot  during  the  whole  period  of  deposition,  but 
has  disappeared  and  reappeared,  perhaps  many  times, 
during  the  same  geological  period.  Consequently  .if  it 
were  to  undergo  a  considerable  amount  of  modification 
during  the  deposition  of  any  one  geological  formation, 
a  section  would  not  include  all  the  fine  intermediate 
gradations  which  must  on  our  theory  have  existed,  but 
abrupt,  though  perhaps  slight,  changes  of  form. 

It  is  all-important  to  remember  that  naturalists  have 
no  golden  rule  by  which  to  distinguish  species  and 
varieties;  they  grant  some  little  variability  to  each 
species,  but  when  they  meet  with  a  somewhat  greater 
amount  of  difference  between  any  two  forms,  they  rank 
both  as  species,  unless  they  are  enabled  to  connect  them 
together  by  the  closest  intermediate  gradations;  and 
this,  from  the  reasons  just  assigned,  we  can  seldom 
hope  to  effect  in  any  one  geological  section.  Supposing 
B  and  C  to  be  two  species,  and  a  third,  A,  to  be  found  in 
an  older  and  underlying  bed;  even  if  A  were  strictly 
intermediate  between  B  and  C,  it  would  simply  be 
ranked  as  a  third  and  distinct  species,  unless  at  the 
same  time  it  could  be  closely  connected  by  interme- 
diate varieties  with  either  one  or  both  forms.  Nor 
should  it  be  forgotten,  as  before  explained,  that  A 
might  be  the  actual  progenitor  of  B  and  C,  and  yet 
would  not  necessarily  be  strictly  intermediate  between 


CHAP.X.]         IN  ANY  SINGLE  FORMATION.  71 

them  in  all  respects.  So  that  we  might  obtain  the 
parent-species  and  its  several  modified  descendants  from 
the  lower  and  upper  beds  of  the  same  formation,  and  un- 
less we  obtained  numerous  transitional  gradations,  we 
should  not  recognise  their  blood-relationship,  and 
should  consequently  rank  them  as  distinct  species. 

It  is  notorious  on  what  excessively  slight  differences 
many  palaeontologists  have  founded  their  species;  and 
they  do  this  the  more  readily  if  the  specimens  come 
from  different  sub-stages  of  the  same  formation.  Some 
experienced  conchologists  are  now  sinking  many  of  the 
very  fine  species  of  D'Orbigny  and  others  into  the 
rank  of  varieties;  and  on  this  view  we  do  find  the  kind 
of  evidence  of  change  which  on  the  theory  we  ought  to 
find.  Look  again  at  the  later  tertiary  deposits,  which 
include  many  shells  believed  by  the  majority  of  natu- 
ralists to  be  identical  with  existing  species;  but  some 
excellent  naturalists,  as  Agassiz  and  Pictet,  maintain 
that  all  these  tertiary  species  are  specifically  distinct, 
though  the  distinction  is  admitted  to  be  very  slight;  so 
that  here,  unless  we  believe  that  these  eminent  natu- 
ralists have  been  misled  by  their  imaginations,  and 
that  these  late  tertiary  species  really  present  no  dif- 
ference whatever  from  their  living  representatives,  or 
unless  we  admit,  in  opposition  to  the  judgment  of  most 
naturalists,  that  these  tertiary  species  are  all  truly  dis- 
tinct from  the  recent,  we  have  evidence  of  the  frequent 
occurrence  of  slight  modifications  of  the  kind  required. 
If  we  look  to  rather  wider  intervals  of  time,  namely, 
to  distinct  but  consecutive  stages  of  the  same  great 
formation,  we  find  that  the  embedded  fossils,  though 
universally  ranked  as  specifically  different,  yet  are  far 
more  closely  related  to  each  other  than  are  the  species 


72  ABSENCE  OF  INTERMEDIATE  VARIETIES  [CHAP.  X. 

found  in  more  widely  separated  formations;  so  that 
here  again  we  have  undoubted  evidence  of  change  in 
the  direction  required  by  the  theory;  but  to  this  latter 
subject  I  shall  return  in  the  following  chapter. 

With  animals  and  plants  that  propagate  rapidly  and 
do  not  wander  much,  there  is  reason  to  suspect,  as  we 
have  formerly  seen,  that  their  varieties  are  generally  at 
first  local;  and  that  such  local  varieties  do  not  spread 
widely  and  supplant  their  parent-forms  until  they  have 
been  modified  and  perfected  in  some. considerable  de- 
gree. According  to  this  view,  the  chance  of  discov- 
ering in  a  formation  in  any  one  country  all  the  early 
stages  of  transition  between  any  two  forms,  is  small, 
for  the  successive  changes  are  supposed  to  have  been 
local  or  confined  to  some  one  spot.  Most  marine  ani- 
mals have  a  wide  range;  and  we  have  seen  that  with 
plants  it  is  those  which  have  the  widest  range,  that 
oftenest  present  varieties;  so  that,  with  shells  and  other 
marine  animals,  it  is  probable  that  those  which  had 
the  widest  range,  far  exceeding  the  limits  of  the  known 
geological  formations  in  Europe,  have  oftenest  given 
rise,  first  to  local  varieties  and  ultimately  to  new  spe- 
cies; and  this  again  would  greatly  lessen  the  chance  of 
our  being  able  to  trace  the  stages  of  transition  in  any 
one  geological  formation. 

It  is  a  more  important  consideration,  leading  to  the 
same  result,  as  lately  insisted  on  by  Dr.  Falconer,  name- 
ly, that  the  period  during  which  each  species  under- 
went modification,  though  long  as  measured  by  years, 
was  probably  short  in  comparison  with  that  during 
which  it  remained  without  undergoing  any  change. 

It  should  not  be  forgotten,  that  at  the  present  day, 
with  perfect  specimens  for  examination,  two  forms  can 


CHAP.X.]         IN  ANY  SINGLE  FORMATION.  ?3 

seldom  be  connected  by  intermediate  varieties,  and  thus 
proved  to  be  the  same  species,  until  many  specimens 
are  collected  from  many  places;  and  with  fossil  species 
this  can  rarely  be  done.  We  shall,  perhaps,  best  per- 
ceive the  improbability  of  our  being  enabled  to  con- 
nect species  by  numerous,  fine,  intermediate,  fossil  links, 
by  asking  ourselves  whether,  for  instance,  geologists 
at  some  future  period  will  be  able  to  prove  that  our 
different  breeds  of  cattle,  sheep,  horses,  and  dogs  are 
descended  from  a  single  stock  or  from  several  abori- 
ginal stocks;  or,  again,  whether  certain  sea-shells  in- 
habiting the  shores  of  North  America,  which  are 
ranked  by  some  conchologists  as  distinct  species  from 
their  European  representatives,  and  by  other  con- 
chologists as  only  varieties,  are  really  varieties,  or 
are,  as  it  is  called,  specifically  distinct.  This  could 
be  effected  by  the  future  geologist  only  by  his  discover- 
ing in  a  fossil  state  numerous  intermediate  grada- 
tions; and  such  success  is  improbable  in  the  highest  de- 
gree. 

It  has  been  asserted  over  and  over  again,  by  writers 
who  believe  in  the  immutability  of  species,  that  geology 
yields  no  linking  forms.  This  assertion,  as  we  shall 
see  in  the  next  chapter,  is  certainly  erroneous.  As  Sir 
J.  Lubbock  has  remarked,  "  Every  species  is  a  link 
"  between  other  allied  forms."  If  we  take  a  genus 
having  a  score  of  species,  recent  and  extinct,  and  de- 
stroy four-fifths  of  them,  no  one  doubts  that  the  re- 
mainder will  stand  much  more  distinct  from  each  other. 
If  the  extreme  forms  in  the  genus  happen  to  have  been 
thus  destroyed,  the  genus  itself  will  stand  more  distinct 
from  other  allied  genera.  What  geological  research 
has  not  revealed,  is  the  former  existence  of  infinitely 
31 


74  ABSENCE  OF  INTERMEDIATE  VARIETIES  [CHAP.  X. 

numerous  gradations,  as  fine  as  existing  varieties,  con- 
necting together  nearly  all  existing  and  extinct  species. 
But  this  ought  not  to  be  expected;  yet  this  has  been 
repeatedly  advanced  as  a  most  serious  objection  against 
my  views. 

It  may  be  worth  while  to  sum  up  the  foregoing 
remarks  on  the  causes  of  the  imperfection  of  the  geo- 
logical record  under  an  imaginary  illustration.  The 
Malay  Archipelago  is  about  the  size  of  Europe  from  the 
North  Cape  to  the  Mediterranean,  and  from  Britain  to 
Russia;  and  therefore  equals  all  the  geological  forma- 
tions which  have  been  examined  with  any  accuracy, 
excepting  those  of  the  United  States  of  America.  I 
fully  agree  with  Mr.  Godwin-Austen,  that  the  present 
condition  of  the  Malay  Archipelago,  with  its  numerous 
large  islands  separated  by  wide  and  shallow  seas,  prob- 
ably represents  the  former  state  of  Europe,  whilst 
most  of  our  formations  were  accumulating.  The  Malay 
Archipelago  is  one  of  the  richest  regions  in  organic 
beings;  yet  if  all  the  species  were  to  be  collected  which 
have  ever  lived  there,  how  imperfectly  would  they 
represent  the  natural  history  of  the  world! 

But  we  have  every  reason  to  believe  that  the  ter- 
restrial productions  of  the  archipelago  would  be  pre- 
served in  an  extremely  imperfect  manner  in  the  forma- 
tions which  we  suppose  to  be  there  accumulating.  Not 
many  of  the  strictly  littoral  animals,  or  of  those  which 
lived  on  naked  submarine  rocks,  would  be  embedded; 
and  those  embedded  in  gravel  or  sand  would  not  en- 
dure to  a  distant  epoch.  Wherever  sediment  did  not 
accumulate  on  the  bed  of  the  sea,  or  where  it  did  not 
accumulate  at  a  sufficient  rate  to  protect  organic  bodies 
from  decay,  no  remains  could  be  preserved. 


CHAP.  X.]         IN  ANY  SINGLE  FORMATION.  75 

Formations  rich  in  fossils  of  many  kinds,  and  of 
thickness  sufficient  to  last  to  an  age  as  distant  in  futu- 
rity as  the  secondary  formations  He  in  the  past,  would 
generally  be  formed  in  the  archipelago  only  during 
periods  of  subsidence.  These  periods  of  subsidence 
would  be  separated  from  each  other  by  immense  in- 
tervals of  time,  during  which  the  area  would  be  either 
stationary  or  rising;  whilst  rising,  the  fossiliferous  for- 
mations on  the  steeper  shores  would  be  destroyed,  al- 
most as  soon  as  accumulated,  by  the  incessant  coast- 
action,  as  we  now  see  on  the  shores  of  South  America. 
Even  throughout  the  extensive  and  shallow  seas  with- 
in the  archipelago,  sedimentary  beds  could  hardly  be 
accumulated  of  great  thickness  during  the  periods  of 
elevation,  or  become  capped  and  protected  by  subse- 
quent deposits,  so  as  to  have  a  good  chance  of  enduring 
to  a  very  distant  future.  During  the  periods  of  sub- 
sidence, there  would  probably  be  much  extinction  of  life; 
during  the  periods  of  elevation,  there  would  be  much 
variation,  but  the  geological  record  would  then  be  less 
perfect. 

It  may  be  doubted  whether  the  duration  of  any  one 
great  period  of  subsidence  over  the  whole  or  part  of  the 
archipelago,  together  with  a  contemporaneous  accumu- 
lation of  sediment,  would  exceed  the  average  duration  of 
the  same  specific  forms;  and  these  contingencies  are  in- 
dispensable for  the  preservation  of  all  the  transitional 
gradations  between  any  two  or  more  species.  If  such 
gradations  were  not  all  fully  preserved,  transitional 
varieties  would  merely  appear  as  so  many  new,  though 
closely  allied  species.  It  is  also  probable  that  each 
great  period  of  subsidence  would  be  interrupted  by  os- 
cillations of  level,  and  that  slight  climatal  changes 


76  ABSENCE  OF  INTERMEDIATE  VARIETIES  [CHAP.  X. 

would  intervene  during  such  lengthy  periods;  and  in 
these  cases  the  inhabitants  of  the  archipelago  would 
migrate,  and  no  closely  consecutive  record  of  their 
modifications  could  be  preserved  in  any  one  formation. 

Very  many  of  the  marine  inhabitants  of  the  archi- 
pelago now  range  thousands  of  miles  beyond  its  con- 
fines; and  analogy  plainly  leads  to  the  belief  that  it 
would  be  chiefly  these  far-ranging  species,  though  only 
some  of  them,  which  would  oftenest  produce  new  varie- 
ties; and  the  varieties  would  at  first  be  local  or  con- 
fined to  one  place,  but  if  possessed  of  any  decided  ad- 
vantage, or  when  further  modified  and  improved,  they 
would  slowly  spread  and  supplant  their  parent-forms. 
When  such  varieties  'returned  to  their  ancient  homes, 
as  they  would  differ  from  their  former  state  in  a  nearly 
uniform,  though  perhaps  extremely  slight  degree,  and 
as  they  would  be  found  embedded  in  slightly  different 
sub-stages  of  the  same  formation,  they  would,  accord- 
ing to  the  principles  followed  by  many  palaeontologists, 
be  ranked  as  new  and  distinct  species. 

If  then  there  be  some  degree  of  truth  in  these  re- 
marks, we  have  no  right  to  expect  to  find,  in  our  geo- 
logical formations,  an  infinite  number  of  those  fine 
transitional  forms  which,  on  our  theory,  have  connected 
all  the  past  and  present  species  of  the  same  group  into 
one  long  and  branching  chain  of  life.  We  ought  only 
to  look  for  a  few  links,  and  such  assuredly  we  do  find — 
some  more  distantly,  some  more  closely,  related  to 
each  other;  and  these  links,  let  them  be  ever  so  close, 
if  found  in  different  stages  of  the  same  formation, 
would,  by  many  paleontologists,  be  ranked  as  distinct 
species.  But  I  do  not  pretend  that  I  should  ever  have 
suspected  how  poor  was  the  record  in  the  best  preserved 


CHAP.X.]         IN  ANY  SINGLE  FORMATION.  77 

geological  sections,  had  not  the  absence  of  innumerable 
transitional  links  between  the  species  which  lived  at 
the  commencement  and  close  of  each  formation,  pressed 
so  hardly  on  my  theory. 

On  the  sudden  Appearance  of  whole  Groups  of  allied 
Species. 

The  abrupt  manner  in  which  whole  groups  of  spe- 
cies suddenly  appear  in  certain  formations,  has  been 
urged  by  several  palaeontologists — for  instance,  by  Agas- 
siz,  Pictet,  and  Sedgwick — as  a  fatal  objection  to  the  be- 
lief in  the  transmutation  of  species.  If  numerous  spe- 
cies, belonging  to  the  same  genera  or  families,  have 
really  started  into  life  at  once,  the  fact  would  be  fatal  to 
the  theory  of  evolution  through  natural  selection.  For 
the  development  by  this  means  of  a  group  of  forms,  all 
of  which  are  descended  from  some  one  progenitor,  must 
have  been  an  extremely  slow  process;  and  the  progeni- 
tors must  have  lived  long  before  their  modified  descen- 
dants. But  we  continually  overrate  the  perfection  of 
the  geological  record,  and  falsely  infer,  because  certain 
genera  or  families  have  not  been  found  beneath  a  cer- 
tain stage,  that  they  did  not  exist  before  that  stage. 
In  all  cases  positive  palasontological  evidence  may  be 
implicitly  trusted;  negative  evidence  is  worthless,  as 
experience  has  so  often  shown.  We  continually  forget 
how  large  the  world  is,  compared  with  the  area  over 
which  our  geological  formations  have  been  carefully 
examined;  we  forget  that  groups  of  species  may  else- 
where have  long  existed,  and  have  slowly  multiplied, 
before  they  invaded  the  ancient  archipelagoes  of  Europe 
and  the  United  States.  We  do  not  make  due  allowance 


78  SUDDEN  APPEARANCE  OF  [CHAP.  X. 

for  the  intervals  of  time  which  have  elapsed  between 
our  consecutive  formations, — longer  perhaps  in  many 
cases  than  the  time  required  for  the  accumulation  of 
each  formation.  These  intervals  will  have  given  time 
for  the  multiplication  of  species  from  some  one  parent- 
form:  and  in  the  succeeding  formation,  such  groups  or 
species  will  appear  as  if  suddenly  created. 

I  may  here  recall  a  remark  formerly  made,  namely, 
that  it  might  require  a  long  succession  of  ages  to  adapt 
an  organism  to  some  new  and  peculiar  line  of  life,  for 
instance,  to  fly  through  the  air;  and  consequently  that 
the  transitional  forms  would  often  long  remain  con- 
fined to  some  one  region;  but  that,  when  this  adapta- 
tion had  once  been  effected,  and  a  few  species  had  thus 
acquired  a  great  advantage  over  other  organisms,  a 
comparatively  short  time  would  be  necessary  to  produce 
many  divergent  forms,  which  would  spread  rapidly  and 
widely,  throughout  the  world.  Professor  Pictet,  in  his 
excellent  Review  of  this  work,  in  commenting  on  early 
transitional  forms,  and  taking  birds  as  an  illustration, 
cannot  see  how  the  successive  modifications  of  the  an- 
terior limbs  of  a  supposed  prototype  could  possibly 
have  been  of  any  advantage.  But  look  at  the  penguins 
of  the  Southern  Ocean;  have  not  these  birds  their  front 
limbs  in  this  precise  intermediate  state  of  "  neither  true 
"arms  nor  true  wings"?  Yet  these  birds  hold  their 
place  victoriously  in  the  battle  for  life;  for  they  exist 
in  infinite  numbers  and  of  many  kinds.  I  do  not  sup- 
pose that  we  here  see  the  real  transitional  grades 
through  which  the  wings  of  birds  have  passed;  but 
what  special  difficulty  is  there  in  believing  that  it 
might  profit  the  modified  descendants  of  the  penguin, 
first  to  become  enabled  to  flap  along  the  surface  of  the 


CHAP.  X].        GROUPS  OF  ALLIED  SPECIES.  79 

sea  like  the  logger-headed  duck,  and  ultimately  to  rise 
from  its  surface  and  glide  through  the  air? 

I  will  now  give  a  few  examples  to  illustrate  the 
foregoing  remarks,  and  to  show  how  liable  we  are  to 
error  in  supposing  that  whole  groups  of  species  have 
suddenly  been  produced.  Even  in  so  short  an  interval 
as  that  between  the  first  and  second  editions  of  Pietet's 
great  work  on  Palaeontology,  published  in  1844-46  and 
in  1853-57,  the  conclusions  on  the  first  appearance  and 
disappearance  of  several  groups  of  animals  have  been 
considerably  modified;  and  a  third  edition  would  re- 
quire still  further  changes.  I  may  recall  the  well- 
known  fact  that  in  geological  treatises,  published  not 
many  years  ago,  mammals  were  always  spoken  of  as 
having  abruptly  come  in  at  the  commencement  of  the 
tertiary  series.  And  now  one  of  the  richest  known  ac- 
cumulations of  fossil  mammals  belongs  to  the  middle  of 
the  secondary  series;  and  true  mammals  have  been  dis- 
covered in  the  new  red  sandstone  at  nearly  the  com- 
mencement of  this  great  series.  Cuvier  used  to  urge 
that  no  monkey  occurred  in  any  tertiary  stratum;  but 
now  extinct  species  have  been  discovered  in  India,  South 
America  and  in  Europe,  as  far  back  as  the  miocene 
stage.  HadMt  not  been  for  the  rare  accident  of  the  pres- 
ervation of  the  footsteps  in  the  new  red  sandstone  of  the 
United  States,  who  would  have  ventured  to  suppose  that 
no  less  than  at  least  thirty  different  bird-like  animals, 
some  of  gigantic  size,  existed  during  that  period?  Not 
a  fragment  of  bone  has  been  discovered  in  these  beds. 
Not  long  ago,  palaeontologists  maintained  that  the 
whole  class  of  birds  came  suddenly  into  existence  during 
the  eocene  period;  but  now  we  know,  on  the  authority 
of  Professor  Owen,  that  a  bird  certainly  lived  during 


80  SUDDEN  APPEARANCE  OP  [CHAP.  X. 

the  deposition  of  the  upper  greensand;  and  still  more 
recently,  that  strange  bird,  the  Archeopteryx,  with  a 
long  lizard-like  tail,  bearing  a  pair  of  feathers  on  each 
joint,  and  with  its  wings  furnished  with  two  free  claws, 
has  been  discovered  in  the  oolitic  slates  of  Solenhofen. 
Hardly  any  recent  discovery  shows  more  forcibly  than 
this,  how  little  we  as  yet  know  of  the  former  inhabitants 
of  the  world. 

I  may  give  another  instance,  which,  from  having 
passed  under  my  own  eyes,  has  much  struck  me.  In  a 
memoir  on  Fossil  Sessile  Cirripedes,  I  stated  that,  from 
the  large  number  of  existing  and  extinct  tertiary  spe- 
cies; from  the  extraordinary  abundance  of  the  indi- 
viduals of  many  species  t  all  over  the  world,  from  the 
Arctic  regions  to  the  equator,  inhabiting  various  zones 
of  depths  from  the  upper  tidal  limits  to  50  fathoms; 
from  the  perfect  manner  in  which  specimens  are  pre- 
served in  the  oldest  tertiary  beds;  from  the  ease  with 
which  even  a  fragment  of  a  valve  can  be  recognised;  from 
all  these  circumstances,  I  inferred  that,  had  sessile  cirri- 
pedes  existed  during  the  secondary  periods,  they  would 
certainly  have  been  preserved  and  discovered;  and  as 
not  one  species  had  then  been  discovered  in  beds  of 
this  age,  I  concluded  that  this  great  group  had  been 
suddenly  developed  at  the  commencement  of  the  ter- 
tiary series.  This  was  a  sore  trouble  to  me,  adding  as 
I  then  thought  one  more  instance  of  the  abrupt  ap- 
pearance of  a  great  group  of  species.  But  my  work  had 
hardly  been  published,  when  a  skilful  palaeontologist, 
M.  Bosquet,  sent  me  a  drawing  of  a  perfect  specimen 
of  an  unmistakable  sessile  cirripede,  which  he  had  him- 
self extracted  from  the  chalk  of  Belgium.  And,  as 
if  to  make  the  case  as  striking  as  possible,  this  cirripede 


CHAP.  X.]        GROUPS  OF  ALLIED  SPECIES.  81 

was  a  Chthamalus,  a  very  common,  large,  and  ubiqui- 
tous genus,  of  which  not  one  species  has  as  yet  been 
found  even  in  any  tertiary  stratum.  Still  more  re- 
cently, a  Pyrgoma,  a  member  of  a  distinct  sub-family  of 
sessile  cirripedes,  has  been  discovered  by  Mr.  Wood- 
ward in  the  upper  chalk;  so  that  we  now  have  abun- 
dant evidence  of  the  existence  of  this  group  of  animals 
during  the  secondary  period. 

The  case  most  frequently  insisted  on  by  palaeonto- 
logists of  the  apparently  sudden  appearance  of  a  whole 
group  of  species,  is  that  of  the  teleostean  fishes,  low 
down,  according  to  Agassiz,  in  the  Chalk  period.  This 
group  includes  the  large  majority  of  existing  species. 
But  certain  Jurassic  and  Triassic  forms  are  now  com- 
monly admitted  to  be  teleostean;  and  even  some  palaeo- 
zoic forms  have  thus  been  classed  by  one  high  authority. 
If  the  teleosteans  had  really  appeared  suddenly  in  the 
northern  hemisphere  at  the  commencement  of  the  chalk 
formation  the  fact  would  have  been  highly  remarkable; 
but  it  would  not  have  formed  an  insuperable  difficulty, 
unless  it  could  likewise  have  been  shown  that  at  the 
same  period  the  species  were  suddenly  and  simultane- 
ously developed  in  other  qu'arters  of  the  world.  It 
is  almost  superfluous  to  remark  that  hardly  any  fossil- 
fish  are  known  from  south  of  the  equator;  and  by  run- 
ning through  Pictet's  Palaeontology  it  will  be  seen  that 
very  few  species  are  known  from  several  formations 
in  Europe.  Some  few  families  of  fish  now  have  a  con- 
fined range;  the  teleostean  fishes  might  formerly  have 
had  a  similarly  confined  range,  and  after  having  been 
largely  developed  in  some  one  sea,  have  spread  widely. 
Nor  have  we  any  right  to  suppose  that  the  seas  of  the 
world  have  always  been  so  freely  open  from  south  to 


82  '     GROUPS  OF  ALLIED  SPECIES        [CHAP.  X. 

north  as  they  are  at  present.  Even  at  this  day,  if 
the  Malay  Archipelago  were  converted  into  land,  the 
tropical  parts  of  the  Indian  Ocean  would  form  a 
large  and  perfectly  enclosed  basin,  in  which  any  great 
group  of  marine  animals  might  be  multiplied;  and 
here  they  would  remain  confined,  until  some  of  the 
species  became  adapted  to  a  cooler  climate,  and 
were  enable  to  double  the  Southern  capes  of  Af- 
rica or  Australia,  and  thus  reach  other  and  distant 


From  these  considerations,  from  our  ignorance  of 
the  geology  of  other  countries  beyond  the  confines  of 
Europe  and  the  United  States,  and  from  the  revolution 
in  our  palasontological  knowledge  effected  by  the  dis- 
coveries of  the  last  dozen  years,  it  seems  to  me  to  be 
about  as  rash  to  dogmatize  on  the  succession  of  organic 
forms  throughout  the  world,  as  it  would  be  for  a  natura- 
list to  land  for  five  minutes  on  a  barren  point  in  Aus- 
tralia, and  then  to  discuss  the  number  and  range  of  its 
productions. 

On  the  sudden  Appearance  of  Groups  of  allied  Species 
in  the  lowest  known  Fossiliferous  Strata. 

There  is  another  and  allied  difficulty,  which  is  much 
more  serious.  I  allude  to  the  manner  in  which  species 
belonging  to  several  of  the  main  divisions  of  the  animal 
kingdom  suddenly  appear  in  the  lowest  known  fossili- 
ferous  rocks.  Most  of  the  arguments  which  have  con- 
vinced me  that  all  the  existing  species  of  the  same  group 
are  descended  from  a  single  progenitor,  apply  with 
equal  force  to  the  earliest  known  species.  For  in- 
stance, it  cannot  be  doubted  that  all  the  Cambrian  and 


CHAP.  X.]  IN  LOWEST  FOSSILIFEROUS  STRATA.          33 

Silurian  trilobites  are  descended  from  some  one  crusta- 
cean, which  must  have  lived  long  before  the  Cambrian 
age,  and  which  probably  differed  greatly  from  any 
known  animal.  Some  of  the  most  ancient  animals,  as 
the  Nautilus,  Lingula,  &c.,  do  not  differ  much  from 
living  species;  and  it  cannot  on  our  theory  be  supposed, 
that  these  old  species  were  the  progenitors  of  all  the 
species  belonging  to  the  same  groups  which  have  sub- 
sequently appeared,  for  they  are  not  in  any  degree  in- 
termediate in  character. 

Consequently,  if  the  theory  be  true,  it  is  indisputable 
that  before  the  lowest  Cambrian  stratum  was  deposited 
long  periods  elapsed,  as  long  as,  or  probably  far  longer 
than,  the  whole  interval  from  the  Cambrian  age  to  the 
present  day;  and  that  during  these  vast  periods  the 
world  swarmed  with  living  creatures.  Here  we  en- 
counter a  formidable  objection;  for  it  seems  doubtful 
whether  the  earth,  in  a  fit  state  for  the  habitation  of 
living  creatures,  has  lasted  long  enough.  Sir  W. 
Thompson  concludes  that  the  consolidation  of  the  crust 
can  hardly  have  occurred  less  than  20  or  more  than 
400  million  years  ago,  but  probably  not  less  than  98  or 
more  than  200  million  years.  These  very  wide  limits 
show  how  doubtful  the  data  are;  and  other  elements 
may  have  hereafter  to  be  introduced  into  the  problem. 
Mr.  Croll  estimates  that  about  60  million  years  have 
elapsed  since  the  Cambrian  period,  but  this,  judging 
from  the  small  amount  of  organic  change  since  the 
commencement  of  the  Glacial  epoch,  appears  a  very 
short  time  for  the  many  and  great  mutations  of  life, 
which  have  certainly  occurred  since  the  Cambrian  for- 
mation; and  the  previous  140  million  years  can  hardly 
be  considered  as  sufficient  for  the  development  of  the 


84:  GROUPS  OF  ALLIED  SPECIES         [CHAP.  X. 

varied  forms  of  life  which  already  existed  during  the 
Cambrian  period.  It  is,  however,  probable,  as  Sir  Wil- 
liam Thompson  insists,  that  the  world  at  a  very  early 
period  was  subjected  to  more  rapid  and  violent  changes 
in  its  physical  conditions  than  those  now  occurring; 
and  such  changes  would  have  tended  to  induce  changes 
at  a  corresponding  rate  in  the  organisms  which  then 
existed. 

To  the  question  why  we  do  not  find  rich  fossiliferous 
deposits  belonging  to  these  assumed  earliest  periods 
prior  to  the  Cambrian  system,  I  can  give  no  satisfactory 
answer.  Several  eminent  geologists,  with  Sir  K.  Mur- 
chison  at  their  head,  were  until  recently  convinced 
that  we  beheld  in  the  organic  remains  of  the  lowest 
Silurian  stratum  the  first  dawn  of  life.  Other  highly 
competent  judges,  as  Lyell  and  E.  Forbes,  have  dis- 
puted this  conclusion.  We  should  not  forget  that  only 
a  small  portion  of  the  world  is  known  with  accuracy. 
Not  very  long  ago  M.  Barrande  added  another  and 
lower  stage,  abounding  with  new  and  peculiar  species, 
beneath  the  then  known  Silurian  system;  and  now, 
still  lower  down  in  the  Lower  Cambrian  formation,  Mr. 
Hicks  has  found  in  South  Wales  beds  rich  in  trilobites, 
and  containing  various  molluscs  and  annelids.  The 
presence  of  phosphatic  nodules  and  bituminous  matter, 
even  in  some  of  the  lowest  azoic  rocks,  probably  indi- 
cates life  at  these  periods;  and  the  existence  of  the 
Eozoon  in  the  Laurentian  formation  of  Canada  is  gener- 
ally admitted.  There  are  three  great  series  of  strata  be- 
neath the  Silurian  system  in  Canada,  in  the  lowest  of 
which  the  Eozoon  is  found.  Sir  W.  Logan  states  that 
their  "  united  thickness  may  possibly  far  surpass  that 
"  of  all  the  succeeding  rocks,  from  the  base  of  the  palao- 


CHAP.  X.]  IN  LOWEST  FOSSILIFEROUS  STRATA.  §5 

"  zoic  series  to  the  present  time.  We  are  thus  carried 
"  back  to  a  period  so  remote,  that  the  appearance  of  the 
"  so-called  Primordial  fauna  (of  Barrande)  may  by  some 
"  be  considered  as  a  comparatively  modern  event."  The 
Eozoon  belongs  to  the  most  lowly  organised  of  all 
classes  of  animals,  but  is  highly  organised  for  its  class; 
it  existed  in  countless  numbers,  and,  as  Dr.  Dawson  has 
remarked,  certainly  preyed  on  other  minute  organic 
beings,  which  must  have  lived  in  great  numbers.  Thus 
the  words,  which  I  wrote  in  1859,  about  the  existence 
of  living  beings  long  before  the  Cambrian  period,  and 
which  are  almost  the  same  with  those  since  used  by  Sir 
W.  Logan,  have  proved  true.  Nevertheless,  the  diffi- 
culty of  assigning  any  good  reason  for  the  absence  of 
vast  piles  of  strata  rich  in  fossils  beneath  the  Cambrian 
system  is  very  great.  It  does  not  seem  probable  that 
the  most  ancient  beds  have  been  quite  worn  away  by 
denudation,  or  that  their  fossils  have  been  wholly  ob- 
literated by  metamorphic  action,  for  if  this  had  been 
the  case  we  should  have  found  only  small  remnants  of 
the  formations  next  succeeding  them  in  age,  and  these 
would  always  have  existed  in  a  partially  metamorphosed 
condition.  But  the  descriptions  which  we  possess  of 
the  Silurian  deposits  over  immense  territories  in  Russia 
and  in  North  America,  do  not  support  the  view,  that 
the  older  a  formation  is,  the  more  invariably  it  has 
suffered  extreme  denudation  and  metamorphism. 

The  case  at  present  must  remain  inexplicable;  and 
may  be  truly  urged  as  a  valid  argument  against  the 
views  here  entertained.  To  show  that  it  may  hereafter 
receive  some  explanation,  I  will  give  the  following  hy- 
pothesis. From  the  nature  of  the  organic  remains 
which  do  not  appear  to  have  inhabited  profound  depths, 


86  GROUPS  OF  ALLIED  SPECIES         [CHAP.  X. 

in  the  several  formations  of  Europe  and  of  the  United 
States;  and  from  the  amount  of  sediment,  miles  in 
thickness,  of  which  the  formations  are  composed,  we 
may  infer  that  from  first  to  last  large  islands  or  tracts 
of  land,  whence  the  sediment  was  derived,  occurred  in 
the  neighbourhood  of  the  now  existing  continents  of 
Europe  and  North  America.  This  same  view  has  since 
been  maintained  by  Agassiz  and  others.  But  we  do  not 
know  what  was  the  state  of  things  in  the  intervals  be- 
tween the  several  successive  formations;  whether  Europe 
and  the  United  States  during  these  intervals  existed  as 
dry  land,  or  as  a  submarine  surface  near  land,  on  which 
sediment  was  not  deposited,  or  as  the  bed  of  an  open  and 
unfathomable  sea. 

Looking  to  the  existing  oceans,  which  are  thrice  as 
extensive  as  the  land,  we  see  them  studded  with  many 
islands;  but  hardly  one  truly  oceanic  island  (with  the 
exception  of  New  Zealand,  if  this  can  be  called  a  truly 
oceanic  island)  is  as  yet  known  to  afford  even  a  remnant 
of  any  palaeozoic  or  secondary  formation.  Hence  we 
may  perhaps  infer,  that  during  the  palaeozoic  and  sec- 
ondary periods,  neither  continents  nor  continental  is- 
lands existed  where  our  oceans  now  extend;  for  had 
they  existed,  palaeozoic  and  secondary  formations  would 
in  all  probability  have  been  accumulated  from  sediment 
derived  from  their  wear  and  tear;  and  these  would  have 
been  at  least  partially  upheaved  by  the  oscillations  of 
level,  which  must  have  intervened  during  these  enor- 
mously long  periods.  If  then  we  may  infer  anything 
from  these  facts,  we  may  infer  that,  where  our  oceans 
now  extend,  oceans  have  extended  from  the  remotest 
period  of  which  we  have  any  record;  and  on  the  other 
hand,  that  where  continents  now  exist,  large  tracts  of 


CHAP.  X.]  IN  LOWEST  FOSSILIFEROUS  STRATA.  87 

land  have  existed,  subjected  no  doubt  to  great  oscilla- 
tions of  level,  since  the  Cambrian  period.  The  col- 
oured map  appended  to  my  volume  on  Coral  Eeefs,  led 
me  to  conclude  that  the  great  oceans  are  still  mainly 
areas  of  subsidence,  the  great  archipelagoes  still  areas  of 
oscillations  of  level,  and  the  continents  areas  of  eleva- 
tion. But  we  have  no  reason  to  assume  that  things  have 
thus  remained  from  the  beginning  of  the  world.  Our 
continents  seem  to  have  been  formed  by  a  preponder- 
ance, during  many  oscillations  of  level,  of  the  force  of 
elevation;  but  may  not  the  areas  of  preponderant  move- 
ment have  changed  in  the  lapse  of  ages?  At  a  period 
long  antecedent  to  the  Cambrian  epoch,  continents  may 
have  existed  where  oceans  are  now  spread  out;  and  clear 
and  open  oceans  may  have  existed  where  our  continents 
now  stand.  Nor  should  we  be  justified  in  assuming 
that  if,  for  instance,  the  bed  of  the  Pacific  Ocean  were 
now  converted  into  a  continent  we  should  there  find 
sedimentary  formations  in  a  recognisable  condition  older 
than  the  Cambrian  strata,  supposing  such  to  have  been 
formerly  deposited; 'for  it  might  well  happen  that  strata 
which  had  subsided  some  miles nearerto  the  centre  of  the 
earth,  and  which  had  been  pressed  on  by  an  enormous 
weight  of  superincumbent  water,  might  have  undergone 
far  more  metamorphic  action  than  strata  which  have  al- 
ways remained  nearer  to  the  surface.  The  immense 
areas  in  some  parts  of  the  world,  for  instance  in  South 
America,  of  naked  metamorphic  rocks,  which  must  have 
been  heated  under  great  pressure,  have  always  seemed  to 
me  to  require  some  special  explanation;  and  we  may  per- 
haps believe  that  we  see  in  these  large  areas,  the  many 
formations  long  anterior  to  the  Cambrian  epoch  in  a 
completely  metamorphosed  and  denuded  condition. 


S3  IMPERFECTION  OF  GEOLOGICAL  RECORD.  [CHAP.  X. 

The  several  difficulties  here  discussed,  namely — that, 
though  we  find  in  our  geological  formations  many  links 
between  the  species  which  now  exist  and  which  formerly 
existed,  we  do  not  find  infinitely  numerous  fine  transi- 
tional forms  closely  joining  them  all  together; — the 
sudden  manner  in  which  several  groups  of  species  first 
appear  in  our  European  formations; — the  almost  entire 
absence,  as  at  present  known,  of  formations  rich  in  fos- 
sils beneath  the  Cambrian  strata, — are  all  undoubtedly 
of  the  most  serious  nature.  We  see  this  in  the  fact  that 
the  most  eminent  paleontologists,  namely,  Cuvier, 
Agassiz,  Barrande,  Pictet,  Falconer,  E.  Forbes,  &c.,  and 
all  our  greatest  geologists,  as  Lyell,  Murchison,  Sedgwick, 
&c.,  have  unanimously,  often  vehemently,  maintained 
the  immutability  of  species.  But  Sir  Charles  Lyell 
now  gives  the  support  of  his  high  authority  to  the  op- 
posite side;  and  most  geologists  and  paleontologists  are 
much  shaken  in  their  former  belief.  Those  who  believe 
that  the  geological  record  is  in  any  degree  perfect,  will 
undoubtedly  at  once  reject  the  theory.  For  my  part, 
following  out  Lyell's  metaphor,  I  look  at  the  geological 
record  as  a  history  of  the  world  imperfectly  kept,  and 
written  in  a  changing  dialect;  of  this  history  we  pos- 
sess the  last  volume  alone,  relating  only  to  two  or  three 
countries.  Of  this  volume,,  only  here  and  there  a  short 
chapter  has  been  preserved;  and  of  each  page,  only  here 
and  there  a  few  lines.  Each  word  of  the  slowly-changing 
language,  more  or  less  different  in  the  successive  chap- 
ters, may  represent  the  forms  of  life,  which  are  en- 
tombed in  our  consecutive  formations,  and  which  falsely 
appear  to  have  been  abruptly  introduced.  On  this 
view,  the  difficulties  above  discussed  are  greatly  dimin- 
ished, or  even  disappear. 


CHAP.  XL]  SUCCESSION  OF  ORGANIC  BEINGS.  89 


CHAPTER   XI. 

ON    THE    GEOLOGICAL    SUCCESSION    OF    ORGANIC  BEINGS. 

On  the  slow  and  successive  appearance  of  new  species — On  their 
different  rates  of  change — Species  once  lost  do  not  reappear — 
Groups  of  species  follow  the  same  general  rules  in  their  ap- 
pearance and  disappearance  as  do  single  species — On  extinction 
— On  simultaneous  changes  in  the  forms  of  life  throughout  the 
world— On  the  affinities  of  extinct  species  to  each  other  and  to 
living  species — On  the  state  of  development  of  ancient  forms — 
On  the  succession  of  the  same  types  within  the  same  areas — 
Summary  of  preceding  and  present  chapter. 

LET  us  now  see  whether  the  several  facts  and  laws 
relating  to  the  geological  succession  of  organic  beings 
accord  best  with  the  common  view  of  the  immutability 
of  species,  or  with  that  of  their  slow  and  gradual  modi- 
fication, through  variation  and  natural  selection. 

New  species  have  appeared  very  slowly,  one  after 
another,  both  on  the  land  and  in  the  waters.  Lyell  has 
shown  that  it  is  hardly  possible  to  resist  the  evidence  on 
this  head  in  the  case  of  the  several  tertiary  stages;  and 
every  year  tends  to  fill  up  the  blanks  between  the  stages, 
and  to  make  the  proportion  between  the  lost  and  exist- 
ing forms  more  gradual.  In  some  of  the  most  recent 
beds,  though  undoubtedly  of  high  antiquity  if  measured 
by  years,  only  one  or  two  species  are  extinct,  and  only 
one  or  two  are  new,  having  appeared  there  for  the  first 
time,  either  locally,  or,  as  far  as  we  know,  on  the  face  of 
the  earth.  The  secondary  formations  are  more  broken; 


90  THE  GEOLOGICAL  SUCCESSION      [CHAP.  XI. 

but,  as  Bronn  has  remarked,  neither  the  appearance 
nor  disappearance  of  the  many  species  embedded  in 
each  formation  has  been  simultaneous. 

Species  belonging  to  different  genera  and  classes  have 
not  changed  at  the  same  rate,  or  in  the  same  degree. 
In  the  older  tertiary  beds  a  few  living  shells  may  still 
be  found  in  the  midst  of  a  multitude  of  extinct  forms. 
Falconer  has  given  a  striking  instance  of  a  similar  fact, 
for  an  existing  crocodile  is  associated  with  many  lost 
mammals  and  reptiles  in  the  sub-Himalayan  deposits. 
The  Silurian  Lingula  differs  but  little  from  the  living 
species  of  this  genus;  whereas  most  of  the  other  Silurian 
Molluscs  and  all  the  Crustaceans  have  changed  greatly. 
The  productions  of  the  land  seem  to  have  changed  at  a 
quicker  rate  than  those  of  the  sea,  of  which  a  striking 
instance  has  been  observed  in  Switzerland.  There  is 
some  reason  to  believe  that  organisms  high  in  the  scale, 
change  more  quickly  than  those  that  are  low:  though 
there  are  exceptions  to  this  rule.  The  amount  of  or- 
ganic change,  as  Pictet  has  remarked,  is  not  the  same  in 
each  successive  so-called  formation.  Yet  if  we  compare 
any  but  the  most  closely  related  formations,  all  the  spe- 
cies will  be  found  to  have  undergone  some  change. 
When  a  species  has  once  disappeared  from  the  face  of 
the  earth,  we  have  no  reason  to  believe  that  the  same 
identical  form  ever  reappears.  The  strongest  apparent 
exception  to  this  latter  rule  is  that  of  the  so-called 
"  colonies  "  of  M.  Barrande,  which  intrude  for  a  period 
in  the  midst  of  an  older  formation,  and  then  allow  the 
pre-existing  fauna  to  reappear;  but  Lyell's  explanation, 
namely,  that  it  is  a  case  of  temporary  migration  from  a 
distinct  geographical  province,  seems  satisfactory. 

These  several  facts  accord  well  with  our  theory, 


CHAP.  XI.]  OP  ORGANIC  BEINGS.  91 

which  includes  no  fixed  law  of  development,  causing  all 
the  inhabitants  of  an  area  to  change,  abruptly,  or  simul- 
taneously, or  to  an  equal  degree.  The  process  of  modi- 
fication must  be  slow,  and  will  generally  effect  only  a 
few  species  at  the  same  time;  for  the  variability  of  each 
species  is  independent  of  that  of  all  others.  Whether 
such  variations  or  individual  differences  as  may  arise 
will  be  accumulated  through  natural  selection  in  a 
greater  or  less  degree,  thus  causing  a  greater  or  less 
amount  of  permanent  modification,  will  depend  on  many 
complex  contingencies — on  the  variations  being  of  a 
beneficial  nature,  on  the  freedom  of  intercrossing,  on 
the  slowly  changing  physical  conditions  of  the  country, 
on  the  immigration  of  new  colonists,  and  on  the  nature 
of  the  other  inhabitants  with  which  the  varying  species 
come  into  competition.  Hence  it  is  by  no  means  sur- 
prising that  one  species  should  retain  the  same  identi- 
cal form  much  longer  than  others;  or,  if  changing, 
should  change  in  a  less  degree.  We  find  similar  rela- 
tions between  the  existing  inhabitants  of  distinct  coun- 
tries; for  instance,  the  land-shells  and  coleopterous  in- 
sects of  Madeira  have  come  to  differ  considerably  from 
their  nearesf  allies  on  the  continent  of  Europe,  whereas 
the  marine  shells  and  birds  have  remained  unaltered. 
We  can  perhaps  understand  the  apparently  quicker  rate 
of  change  in  terrestrial  and  in  more  highly  organised 
productions  compared  with  marine  and  lower  produc- 
tions, by  the  more  complex  relations  of  the  higher 
beings  to  their  organic  and  inorganic  conditions  of  life, 
as  explained  in  a  former  chapter.  When  many  of  the 
inhabitants  of  any  area  have  become  modified  and  im- 
proved, we  can  understand,  on  the  principle  of  compe- 
tition, and  from  the  all-important  relations  of  organ- 


92  THE  GEOLOGICAL  SUCCESSION      [CHAP.  XL 

ism  to  organism  in  the  struggle  for  life,  that  any  form 
which  did  not  become  in  some  degree  modified  and  im- 
proved, would  be  liable  to  extermination.  Hence  we  see 
why  all  the  species  in  the  same  region  do  at  last,  if  we 
look  to  long  enough  intervals  of  time,  become  modified, 
for  otherwise  they  would  become  extinct. 

In  members  of  the  same  class  the  average  amount  of 
change,  during  long  and  equal  periods  of  time,  may, 
perhaps,  be  nearly  the  same;  but  as  the  accumulation 
of  enduring  formations,  rich  in  fossils,  depends  on  great 
masses  of  sediment  being  deposited  on  subsiding  areas, 
our  formations  have  been  almost  necessarily  accumu- 
lated at  wide  and  irregularly  intermittent  intervals  of 
time;  consequently  the  amount  of  organic  change  ex- 
hibited by  the  fossils  embedded  in  consecutive  forma- 
tions is  not  equal.  Each  formation,  on  this  view,  does 
not  mark  a  new  and  complete  act  of  creation,  but  only 
an  occasional  scene,  taken  almost  at  hazard,  in  an  ever 
slowly  changing  drama. 

We  can  clearly  understand  why  a  species  when  once 
lost  should  never  reappear,  even  if  the  very  same  con- 
ditions of  life,  organic  and  inorganic,  should  recur. 
For  though  the  offspring  of  one  species  might  be 
adapted  (and  no  doubt  this  has  occurred  in  innumerable 
instances)  to  fill  the  place  of  another  species  in  the  econ- 
omy of  nature,  and  thus  supplant  it;  yet  the  two  forms 
— the  old  and  the  new — would  not  be  identically  the 
same;  for  both  would  almost  certainly  inherit  different 
characters  from 'their  distinct  progenitors;  and  organ- 
isms already  differing  would  vary  in  a  different  manner. 
For  instance,  it  is  possible,  if  all  our  fantail  pigeons 
were  destroyed,  that  fanciers  might  make  a  new  breed 
hardly  distinguishable  from  the  present  breed;  but  if 


CHAP.  XI.]  OF  ORGANIC  BEINGS.  93 

the  parent  rock-pigeon  were  likewise  destroyed,  and 
under  nature  we  have  every  reason  to  believe  that 
parent-forms  are  generally  supplanted  and  exterminated 
by  their  improved  offspring,  it  is  incredible  that  a  fantail, 
identical  with  the  existing  breed,  could  be  raised  from 
any  other  species  of  pigeon,  or  even  from  any  other  well- 
established  race  of  the  domestic  pigeon,  for  the  successive 
variations  would  almost  certainly  be  in  some  degree  dif- 
ferent, and  the  newly-formed  variety  would  probably  in- 
herit from  its  progenitor  some  characteristic  differences. 

Groups  of  species,  that  is,  genera  and  families,  fol- 
low the  same  general  rules  in  their  appearance  and  dis- 
appearance as  do  single  species,  changing  more  or  less 
quickly,  and  in  a  greater  or  lesser  degree.  A  group, 
when  it  has  once  disappeared,  never  reappears;  that  is, 
its  existence,  as  long  as  it  lasts,  is  continuous.  I  am 
aware  that  there  are  some  apparent  exceptions  to  this 
rule,  but  the  exceptions  are  surprisingly  few,  so  few  that 
E.  Forbes,  Pictet,  and  Woodward  (though  all  strongly 
opposed  to  such  views  as  I  maintain)  admit  its  truth; 
and  the  rule  strictly  accords  with  the  theory.  For  all 
the  species  of  the  same  group,  however  long  it  may 
have  lasted,  are  the  modified  descendants  one  from  the 
other,  and  all  from  a  common  progenitor.  In  the  genus 
Lingula,  for  instance,  the  species  which  have  successively 
appeared  at  all  ages  must  have  been  connected  by  an 
unbroken  series  of  generations,  from  the  lowest  Silurian 
stratum  to  the  present  day. 

We  have  seen  in  the  last  chapter  that  whole  groups 
of  species  sometimes  falsely  appear  to  have  been  abrupt- 
ly developed;  and  I  have  attempted  to  give  an  explana- 
tion of  this  fact,  which  if  true  would  be  fatal  to  my 
views.  But  such  cases  are  certainly  exceptional;  the 


91  EXTINCTION.  [CHAP.  XI. 

general  rule  being  a  gradual  increase  in  number,  until 
the  group  reaches  its  maximum,  and  then,  sooner  or 
later,  a  gradual  decrease.  If  the  number  of  the  species 
included  within  a  genus,  or  the  number  of  the  genera 
within  a  family,  be  represented  by  a  vertical  line  of  vary- 
ing thickness,  ascending  through  the  successive  geologi- 
cal formations,  in  which  the  species  are  found,  the  line 
will  sometimes  falsely  appear  to  begin  at  its  lower  end, 
not  in  a  sharp  point,  but  abruptly;  it  then  gradually 
thickens  upwards,  often  keeping  of  equal  thickness  for 
a  space,  and  ultimately  thins  out  in  the  upper  beds, 
marking  the  decrease  and  final  extinction  of  the  species. 
This  gradual  increase  in  number  of  the  species  of  a 
group  is  strictly  conformable  with  the  theory,  for  the 
species  of  the  same  genus,  and  the  genera  of  the  same 
family,  can  increase  only  slowly  and  progressively;  the 
process  of  modification  and  the  production  of  a  number 
of  allied  forms  necessarily  being  a  slow  and  gradual  pro- 
cess,— one  species  first  giving  rise  to  two  or  three  varie- 
ties, these  being  slowly  converted  into  species,  which  in 
their  turn  produce  by  equally  slow  steps  other  varieties 
and  species,  and  so  on,  like  the  branching  of  a  great  tree 
from  a  single  stem,  till  the  group  becomes  large. 

On  Extinction. 

We  have  as  yet  only  spoken  incidentally  of  the  dis- 
appearance of  species  and  of  groups  of  species.  On  the 
theory  of  natural  selection,  the  extinction  of  old  forms 
and  the  production  of  new  and  improved  forms  are 
intimately  connected  together.  The  old  notion  of  all 
the  inhabitants  of  the  earth  having  been  swept  away  by 
catastrophes  at  successive  periods  is  very  generally  given 
up,  even  by  those  geologists,  as  Elie  de  Beaumont,  Mur- 


CHAP.  XL]  EXTINCTION.  95 

chison,  Barrande,  &c.,  whose  general  views  would  natu- 
rally lead  them  to  this  conclusion.  On  the  contrary, 
we  have  every  reason  to  believe,  from  the  study  of  the 
tertiary  formations,  that  species  and  groups  of  species 
gradually  disappear,  one  after  another,  first  from  one 
spot,  then  from  another,  and  finally  from  the  world.  In 
some  few  cases  however,  as  by  the  breaking  of  an  isth- 
mus and  the  consequent  irruption  of  a  multitude  of  new 
inhabitants  into  an  adjoining  sea,  or  by  the  final  subsi- 
dence of  an  island,  the  process  of  extinction  may  have 
been  rapid.  Both  single  species  and  whole  groups  of 
species  last  for  very  unequal  periods;  some  groups,  as 
we  have  seen,  have  endured  from  the  earliest  known 
dawn  of  life  to  the  present  day;  some  have  disappeared 
before  the  close  of  the  paleozoic  period.  No  fixed  law 
seems  to  determine  the  length  of  time  during  which 
any  single  species  or  any  single  genus  endures.  There 
is  reason  to  believe  that  the  extinction  of  a  whole  group 
of  species  is  generally  a  slower  process  than  their  pro- 
duction: if  their  appearance  and  disappearance  be  rep- 
resented, as  before,  by  a  vertical  line  of  varying  thick- 
ness the  line  is  found  to  taper  more  gradually  at  its  up- 
per end,  which  marks  the  progress  of  extermination, 
than  at  its  lower  end,  which  marks  the  first  appearance 
and  the  e*arly  increase  in  number  of  the  species.  In 
some  cases,  however,  the  extermination  of  whole  groups, 
as  of  ammonites,  towards  the  close  of  the  secondary 
period,  has  been  wonderfully  sudden. 

The  extinction  of  species  has  been  involved  in  the 
most  gratuitous  mystery.  Some  authors  have  even  sup- 
posed that,  as  the  individual  has  a  definite  length  of 
life,  so  have  species  a  definite  duration.  N"o  one  can 
have  marvelled  more  than  I  have  done  at  the  extinction 


96  EXTINCTION.  [CHAP.  XL 

of  species.  When  I  found  in  La  Plata  the  tooth  of  a 
horse  embedded  with  the  remains  of  Mastodon,  Mega- 
therium, Toxodon,  and  other  extinct  monsters,  which 
all  co-existed  with  still  living  shells  at  a  very  late  geo- 
logical period,  I  was  filled  with  astonishment;  for,  see- 
ing that  the  horse,  since  its  introduction  by  the  Span- 
iards into  South  America,  has  run  wild  over  the  whole 
country  and  has  increased  in  numbers  at  an  unparal- 
leled rate,  I  asked  myself  what  could  so  recently  have 
exterminated  the  former  horse  under  conditions  of  life 
apparently  so  favourable.  But  my  astonishment  was 
groundless.  Professor  Owen  soon  perceived  that  the 
tooth,  though  so  like  that  of  the  existing  horse,  be- 
longed to  an  extinct  species.  Had  this  horse  been  still 
living,  but  in  some  degree  rare,  no  naturalist  would 
have  felt  the  least  surprise  at  its  rarity;  for  rarity  is  the 
attribute  of  a  vast  number  of  species  of  all  classes,  in  all 
countries.  If  we  ask  ourselves  why  this  or  that  species 
is  rare,  we  answer  that  something  is  unfavourable  in  its 
conditions  of  life;  but  what  that  something  is  we  can 
hardly  ever  tell.  On  the  supposition  of  the  fossil  horse 
still  existing  as  a  rare  species,  we  might  have  felt  cer- 
tain, from  the  analogy  of  all  other  mammals,  even  of 
the  slow-breeding  elephant,  and  from  the  history  of  the 
naturalisation  of  the  domestic  horse  in  South'  America, 
that  under  more  favourable  conditions  it  would  in  a 
very  few  years  have  stocked  the  whole  continent.  But 
we  could  not  have  told  what  the  unfavourable  condi- 
tions were  which  checked  its  increase,  whether  some  one 
or  several  contingencies,  and  at  what  period  of  the 
horse's  life,  and  in  what  degree  they  severally  acted.  If 
the  conditions  had  gone  on,  however  slowly,  becoming 
less  and  less  favourable,  we  assuredly  should  not  have 


CHAP.  XL]  EXTINCTION.  97 

perceived  the  fact,  yet  the  fossil  horse  would  certainly 
have  become  rarer  and  rarer,  and  finally  extinct; — its 
place  being  seized  on  by  some  more  successful  competitor. 

It  is  most  difficult  always  to  remember  that  the  in- 
crease of  every  creature  is  constantly  being  checked 
by  unperceived  hostile  agencies;  and  that  these  same 
unperceived  agencies  are  amply  sufficient  to  cause  rarity, 
and  finally  extinction.  So  little  is  this  subject  under- 
stood, that  I  have  heard  surprise  repeatedly  expressed 
at  such  great  monsters  as  the  Mastodon  and  the  more 
ancient  Dinosaurians  having  become  extinct;  as  if  mere 
bodily  strength  gave  victory  in  the  battle  of  life.  Mere 
size,  on  the  contrary,  would  in  some  cases  determine,  as 
has  been  remarked  by  Owen,  quicker  extermination 
from  the  greater  amount  of  requisite  food.  Before 
man  inhabited  India  or  Africa,  some  cause  must  have 
checked  the  continued  increase  of  the  existing  elephant. 
A  highly  capable  judge,  Dr.  Falconer,  believes  that  it  is 
chiefly  insects  which,  from  incessantly  harassing  and 
weakening  the  elephant  in  India,  check  its  increase;  and 
this  was  Bruce's  conclusion  with  respect  to  the  African 
elephant  in  Abyssinia.  It  is  certain  that  insects  and 
blood-sucking  bats  determine  the  existence  of  the  larger 
naturalised  quadrupeds  in  several  parts  of  S.  America. 

We  see  in  many  cases  in  the  more  recent  tertiary  for- 
mations, that  rarity  precedes  extinction;  and  we  know 
that  this  has  been  the  progress  of  events  with  those 
animals  which  have  been  exterminated,  either  locally  or 
wholly,  through  man's  agency.  I  may  repeat  what  I 
published  in  1845,  namely,  that  to  admit  that  species 
generally  become  rare  before  they  become  extinct — to 
feel  no  surprise  at  the  rarity  of  a  species,  and  yet  to  mar- 
vel greatly  when  the  species  ceases  to  exist,  is  much  the 


98  EXTINCTION.  [CHAP.  XI. 

same  as  to  admit  that  sickness  in  the  individual  is  the 
forerunner  of  death — to  feel  no  surprise  at  sickness, 
but,  when  the  sick  man  dies,  to  wonder  and  to  suspect 
that  he  died  by  some  deed  of  violence. 

The  theory  of  natural  selection  is  grounded  on  the 
belief  that  each  new  variety  and  ultimately  each  new 
species,  is  produced  and  maintained  by  having  some 
advantage  over  those  with  which  it  comes  into  competi- 
tion; and  the  consequent  extinction  of  the  less-fa- 
voured forms  almost  inevitably  follows.  It  is  the  same 
with  our  domestic  productions;  when  a  new  and  slightly 
improved  variety  has  been  raised,  it  at  first  supplants 
the  less  improved  varieties  in  the  same  neighbourhood; 
when  much  improved  it  is  transported  far  and  near,  like 
our  short-horn  cattle,  and  takes  the  place  of  other 
breeds  in  other  countries.  Thus  the  appearance  of  new 
forms  and  the  disappearance  of  old  forms,  both  those 
naturally  and  those  artificially  produced,  are  bound  to- 
gether. In  flourishing  groups,  the  number  of  new  spe- 
cific forms  which  have  been  produced  within  a  given 
time  has  at  some  periods  probably  been  greater  than  the 
number  of  the  old  specific  forms  which  have  been  ex- 
terminated; but  we  know  that  species  have  not  gone  on 
indefinitely  increasing,  at  least  during  the  "later  geo- 
logical epochs,  so  that,  looking  to  later  times,  we  may 
believe  that  the  production  of  new  forms  has  caused  the 
extinction  of  about  the  same  number  of  old  forms. 

The  competition  will  generally  be  most  severe,  as 
formerly  explained  and  illustrated  by  examples,  between 
the  forms  which  are  most  like  each  other  in  all  respects. 
Hence  the  improved  and  modified  descendants  of  a  spe- 
cies will  generally  cause  the  extermination  of  the  parent- 
species;  and  if  many  new  forms  have  been  developed 


CHAP.  XL]  EXTINCTION.  99 

from  any  one  species,  the  nearest  allies  of  that  species, 
i.e.  the  species  of  the  same  genus,  will  be  the  most  liable 
to  extermination.  Thus,  as  I  believe,  a  number  of  new 
species  descended  from  one  species,  that  is  a  new  genus, 
comes  to  supplant  an  old  genus,  belonging  to  the  same 
family.  But  it  must  often  have  happened  that  a  new 
species  belonging  to  some  one  group  has  seized  on  the 
place  occupied  by  a  species  belonging  to  a  distinct  group, 
and  thus  have  caused  its  extermination.  If  many  allied 
forms  be  developed  from  the  successful  intruder,  many 
will  have  to  yield  their  places;  and  it  will  generally  be 
the  allied  forms,  which  will  suffer  from  some  inherited 
inferiority  in  common.  But  whether  it  be  species  be- 
longing to  the  same  or  to  a  distinct  class,  which  have 
yielded  their  places  to  other  modified  and  improved  spe- 
cies, a  few  of  the  sufferers  may  often  be  preserved  for 
a  long  time,  from  being  fitted  to  some  peculiar  line  of 
life,  or  from  inhabiting  some  distant  and  isolated  station, 
where  they  will  have  escaped  severe  competition.  For 
instance,  some  species  of  Trigonia,  a  great  genus  of  shells 
in  the  secondary  formations,  survive  in  the  Australian 
seas;  and  a  few  members  of  the  great  and  almost  extinct 
group  of  Ganoid  fishes  still  inhabit  our  fresh  waters. 
Therefore  the  utter  extinction  of  a  group  is  generally,  as 
we  have  seen,  a  slower  process  than  its  production. 

With  respect  to  the  apparently  sudden  extermina- 
tion of  whole  families  or  orders,  as  of  Trilobites  at  the 
close  of  the  palaeozoic  period  and  of  Ammonites  at  the 
close  of  the  secondary  period,  we  must  remember  what 
has  been  already  said  on  the  probable  wide  intervals  of 
time  between  our  consecutive  formations;  and  in  these 
intervals  there  may  have  been  much  slow  extermination. 
Moreover,  when,  by  sudden  immigration  or  by  unusu- 


100  FORMS  OF  LIFE  CHANGING         [CHAP.  XI. 

ally  rapid  development,  many  species  of  a  new  group 
have  taken  possession  of  an  area,  many  of  the  older 
species  will  have  been  exterminated  in  a  correspond- 
ingly rapid  manner;  and  the  forms  which  thus  yield 
their  places  will  commonly  be  allied,  for  they  will  par- 
take of  the  same  inferiority  in  common. 

Thus,  as  it  seems  to  me,  the  manner  in  which  single 
species  and  whole  groups  of  species  become  extinct 
accords  well  with  the  theory  of  natural  selection.  We 
need  not  marvel  at  extinction;  if  we  must  marvel,  let 
it  be  at  our  own  presumption  in  imagining  for  a  mo- 
ment that  we  understand  the  many  complex  contin- 
gencies on  which  the  existence  of  each  species  depends. 
If  we  forget  for  an  instant  that  each  species  tends  to 
increase  inordinately,  and  that  some  check  is  always 
in  action,  yet  seldom  perceived  by  us,  the  whole  econ- 
omy of  nature  will  be  utterly  obscured.  Whenever  we 
can  precisely  say  why  this  species  is  more  abundant  in 
individuals  than  that;  why  this  species  and  not  an- 
other can  be  naturalised  in  a  given  country;  then,  and 
not  until  then,  we  may  justly  feel  surprise  why  we  can- 
not account  for  the  extinction  of  any  particular  spe- 
cies or  group  of  species. 

On  the  Forms  of  Life  changing  almost  simultaneously 
throughout  the  World. 

Scarcely  any  palaontological  discovery  is  more 
striking  than  the  fact  that  the  forms  of  life  change 
almost  simultaneously  throughout  the  world.  Thus  our 
European  Chalk  formation  can  be  recognised  in  many 
distant  regions,  under  the  most  different  climates,  where 
not  a  fragment  of  the  mineral  chalk  itself  can  be  found; 
namely  in  North  America,  in  equatorial  South  America, 


CHAP.  XL]         THROUGHOUT  THE  WORLD.  101 

in  Tierra  del  Fuego,  at  the  Cape  of  Good  Hope,  and  in 
the  peninsula  of  India.  For  at  these  distant  points, 
the  organic  remains  in  certain  beds  present  an  unmis- 
takeable  resemblance  to  those  of  the  Chalk.  It  is  not 
that  the  same  species  are  met  with;  for  in  some  cases 
not  one  species  is  identically  the  same,  but  they  be- 
long to  the  same  families,  genera,  and  sections  of  genera, 
and  sometimes  are  similarly  characterised  in  such  trifling 
points  as  mere  superficial  sculpture.  Moreover,  other 
forms,  which  are  not  found  in  the  Chalk  of  Europe, 
but  which  occur  in  the  formations  either  above  or  be- 
low, occur  in  the  same  order  at  these  distant  points 
of  the  world.  In  the  several  successive  palaeozoic  for- 
mations of  Russia,  Western  Europe,  and  North  America, 
a  similar  parallelism  in  the  forms  of  life  has  been  ob- 
served by  several  authors;  so  it  is,  according  to  Lyell, 
with  the  European  and  North  American  tertiary  de- 
posits. Even  if  the  few  fossil  species  which  are  com- 
mon to  the  Old  and  New  "Worlds  were  kept  wholly  out 
of  view,  the  general  parallelism  in  the  successive  forms 
of  life,,  in  the  palaeozoic  and  tertiary  stages,  would  still 
be  manifest,  and  the  several  formations  could  be  easily 
correlated. 

These  observations,  however,  relate  to  the  marine 
inhabitants  of  the  world:  we  have  not  sufficient  data 
to  judge  whether  the  productions  of  the  land  and  of 
fresh  water  at  distant  points  change  in  the  same  parallel 
manner.  We  may  doubt  whether  they  have  thus 
changed:  if  the  Megatherium,  Mylodon,  Macrauchenia, 
and  Toxodon  had  been  brought  to  Europe  from  La  Plata, 
without  any  information  in  regard  to  their  geological 
position,  no  one  would  have  suspected  that  they  had  co- 
existed with  sea-shells  all  still  living;  but  as  these 


102  FORMS  OF  LIFE  CHANGING         [CHAP.  XI. 

anomalous  monsters  co-existed  with  the  Mastodon  and 
Horse,  it  might  at  least  have  been  inferred  that  they 
had  lived  during  one  of  the  later  tertiary  stages. 

When  the  marine  forms  of  life  are  spoken  of  as 
having  changed  simultaneously  throughout  the  world, 
it  must  not  be  supposed  that  this  expression  relates  to 
the  same  year,  or  to  the  same  century,  or  even  that  it 
has  a  very  strict  geological  sense;  for  if  all  the  marine 
animals  now  living  in  Europe,  and  all  those  that  lived 
in  Europe  during  the  pleistocene  period  (a  very  remote 
period  as  measured  by  years,  including  the  whole  gla- 
cial epoch)  were  compared  with  those  now  existing  in 
South  America  or  in  Australia,  the  most  skilful  natu- 
ralist would  hardly  be  able  to  say  whether  the  present 
or  the  pleistocene  inhabitants  of  Europe  resembled  most 
closely  those  of  the  southern  hemisphere.  So,  again, 
several  highly  competent  observers  maintain  that  the 
existing  productions  of  the  United  States  are  more 
closely  related  to  those  which  lived  in  Europe  during 
certain  late  tertiary  stages,  than  to  the  present  inhabi- 
tants of  Europe;  and  if  this  be  so,  it  is  evident  that  fos- 
siliferous  beds  now  deposited  on  the  shores  of  North 
America  would  hereafter  be  liable  to  be  classed  with 
somewhat  older  European  beds.  Nevertheless,  looking 
to  a  remotely  future  epoch,  there  can  be  little  doubt 
that  all  the  more  modern  marine  formations,  namely, 
the  upper  pliocene,  the  pleistocene  and  strictly  modern 
beds  of  Europe,  North  and  South  America,  and  Aus- 
tralia, from  containing  fossil  remains  in  some  degree 
allied,  and  from  not  including  those  forms  which  are 
found  only  in  the  older  underlying  deposits,  would  be 
correctly  ranked  as  simultaneous  in  a  geological  sense. 

The  fact  of  the  forms  of  life  changing  simultaneous- 


CHAP.  XL]        THROUGHOUT  THE  WORLD.  103 

ly,  in  the  above  large  sense,  at  distant  parts  of  the  world, 
has  greatly  struck  these  admirable  observers,  MM.  de 
Verneuil  and  d'Archiac.  After  referring  to  the  parallel- 
ism of  the  paleozoic  forms  of  life  in  various  parts  of 
Europe,  they  add,  "  If,  struck  by  this  strange  sequence, 
we  turn  our  attention  to  North  America,  and  there 
discover  a  series  of  analogous  phenomena,  it  will  appear 
certain  that  all  these  modifications  of  species,  their 
extinction,  and  the  introduction  of  new  ones,  cannot 
be  owing  to  mere  changes  in  marine  currents  or  other 
causes  more  or  less  local  and  temporary,  but  depend  on 
general  laws  which  govern  the  whole  animal  kingdom." 
M.  Barrande  has  made  forcible  remarks  to  precisely 
the  same  effect.  It  is,  indeed,  quite  futile  to  look  to 
changes  of  currents,  climate,  or  other  physical  con- 
ditions, as  the  cause  of  these  great  mutations  in  the 
forms  of  life  throughout  the  world,  under  the  most  dif- 
ferent climates.  We  must,  as  Barrande  has  remarked, 
look  to  some  special  law.  We  shall  see  this  more  clearly 
when  we  treat  of  the  present  distribution  of  organic 
beings,  and  find  how  slight  is  the  relation  between  the 
physical  conditions  of  various  countries  and  the  nature 
of  their  inhabitants.  ^ 

This  great  fact  of  the  parallel  succession  of  the  forms 
of  life  throughout  the  world,  is  explicable  on  the  theory 
of  natural  selection.  New  species  are  formed  by  having 
some  advantage  over  older  forms;  and  the  forms,  which 
are  already  dominant,  or  have  some  advantage  over 
the  other  forms  in  their  own  country,  give  birth  to  the 
greatest  number  of  new  varieties  or  incipient  species. 
We  have  distinct  evidence  on  this  head,  in  the  plants 
which  are  dominant,  that  is,  which  are  commonest  and 
most  widely  diffused,  producing  the  greatest  number  of 


104  FORMS  OF  LIFE  CHANGING         [CHAP.  XI. 

new  varieties.  It  is  also  natural  that  the  dominant, 
varying,  and  far-spreading  species,  which  have  already 
invaded  to  a  certain  extent  the  territories  of  other 
species,  should  be  those  which  would  have  the  best 
chance  of  spreading  still  further,  and  of  giving  rise  in 
new  countries  to  other  new  varieties  and  species.  The 
process  of  diffusion  would  often  be  very  slow,  depending 
on  climatal  and  geographical  changes,  on  strange  acci- 
dents, and  on  the  gradual  acclimatisation  of  new  species 
to  the  various  climates  through  which  they  might  have 
to  pass,  but  in  the  course  of  time  the  dominant  forms 
would  generally  succeed  in  spreading  and  would  ulti- 
mately prevail.  The  diffusion  would,  it  is  probable,  be 
slower  with  the  terrestrial  inhabitants  of  distinct  conti- 
nents than  with  the  marine  inhabitants  of  the  continu- 
ous sea.  We  might  therefore  expect  to  find,  as  we  do 
find,  a  less  strict  degree  of  parallelism  in  the  succesion  of 
the  productions  of  the  land  than  with  those  of  the  sea. 

Thus,  as  it  seems  to  me,  the  parallel,  and,  taken  in  a 
large  sense,  simultaneous,  succession  of  the  same  forms 
of  life  throughout  the  world,  accords  well  with  the 
principle  of  new  species  having  been  formed  by  domi- 
nant species  spreading  widely  and  varying;  the  new 
species  thus  produced  being  themselves  dominant,  ow- 
ing to  their  having  had  some  advantage  over  their  al- 
ready dominant  parents,  as  well  as  over  other  species, 
and  again  spreading,  varying,  and  producing  new  forms. 
The  old  forms  which  are  beaten  and  which  yield  their 
places  to  the  new  and  victorious  forms,  will  generally 
be  allied  in  groups,  from  inheriting  some  inferiority  in 
common;  and  therefore,  as  new  and  improved  groups 
spread  throughout  the  world,  old  groups  disappear  from 
the  world;  and  the  succession  of  forms  everywhere 


CHAP.  XL]         THROUGHOUT  THE  WORLD.  105 

tends  to  correspond  both  in  their  first  appearance  and 
final  disappearance. 

There  is  one  other  remark  connected  with  this  subject 
worth  making.  I  have  given  my  reasons  for  believing 
that  most  of  our  great  formations,  rich  in  fossils,  were 
deposited  during  periods  of  subsidence;  and  that  blank 
intervals  of  vast  duration,  as  far  as  fossils  are  concerned, 
occurred  during  the  periods  when  the  bed  of  the  sea 
was  either  stationary  or  rising,  and  likewise  when  sedi- 
ment was  not  thrown  down  quickly  enough  to  embed 
and  preserve  organic  remains.  During  these  long  and 
blank  intervals  I  suppose  that  the  inhabitants  of  each 
region  underwent  a  considerable  amount  of  modification 
and  extinction,  and  that  there  was  much  migration  from 
other  parts  of  the  world.  As  we  have  reason  to  be- 
lieve that  large  areas  are  affected  by  the  same  move- 
ment, it  is  probable  that  strictly  contemporaneous  for- 
mations have  often  been  accumulated  over  very  wide 
spaces  in  the  same  quarter  of  the  world;  but  we  are 
very  far  from  having  any  right  to  conclude  that  this 
has  invariably  been  the  case,  and  that  large  areas  have 
invariably  been  affected  by  the  same  movements.  "When 
two  formations  have  been  deposited  in  two  regions  dur- 
ing nearly,  but  not  exactly,  the  same  period,  we  should 
find  in  both,  from  the  causes  explained  in  the  fore- 
going paragraphs,  the  same  general  succession  in  the 
forms  of  life;  but  the  species  would  not  exactly  cor- 
respond; for  there  will  have  been  a  little  more  time 
in  the  one  region  than  in  the  other  for  modification, 
extinction,  and  immigration. 

I.  suspect  that  cases  of  this  nature  occur  in  Europe. 
Mr.  Preshvich,  in  his  admirable  Memoirs  on  the  eocene 
deposits  of  England  and  France,  is  able  to  draw  a  close 


106  AFFINITIES  OF  EXTINCT  SPECIES.  [CHAP.  XL 

general  parallelism  between  the  successive  stages  in 
the  two  countries;  but  when  he  compares  certain  stages 
in  England  with  those  in  France,  although  he  finds  in 
both  a  curious  accordance  in  the  numbers  of  the  species 
belonging  to  the  same  genera,  yet  the  species  them- 
selves differ  in  a  manner  very  difficult  to  account  for, 
considering  the  proximity  of  the  two  areas, — unless, 
indeed,  it  be  assumed  that  an  isthmus  separated  two 
seas  inhabited  by  distinct,  but  contemporaneous,  faunas. 
Lyell  has  made  similar  observations  on  some  of  the 
later  tertiary  formations.  Barrande,  also,  shows  that 
there  is  a  striking  general  parallelism  in  'the  successive 
Silurian  deposits  of  Bohemia  and  Scandinavia;  never- 
theless he  finds  a  surprising  amount  of  difference  in 
the  species.  If  the  several  formations  in  these  regions 
have  not  been  deposited  during  the  same  exact  periods, 
— a  formation  in  one  region  often  corresponding  with  a 
blank  interval  in  the  other, — and  if  in  both  regions  the 
species  have  gone  on  slowly  changing  during  the  accu- 
mulation of  the  several  formations  and  during  the  long 
intervals  of  time  between  them;  in  this  case  the  several 
formations  in  the  two  regions  could  be  arranged  in  the 
same  order,  in  accordance  with  the  general  succession 
of  the  forms  of  life,  and  the  order  would  falsely  appear 
to  be  strictly  parallel;  nevertheless  the  species  would 
not  be  all  the  same  in  the  apparently  corresponding 
stages  in  the  two  regions. 

On  the  Affinities  of  Extinct  Species  to  each  other,,  and 
to  Living  Forms. 

Let  us  now  look  to  the  mutual  affinities  of  extinct 
and  living  species.  All  fall  into  a  few  grand  classes; 
and  this  fact  is  at  once  explained  on  the  principle  of 


CHAP.  XL]  AFFINITIES  OF  EXTINCT  SPECIES.  107 

descent.  The  more  ancient  any  form  is,  the  more,  as 
a  general  rule,  it  differs  from  living  forms.  But,  as 
Buckland  long  ago  remarked,  extinct  species  can  all  be 
classed  either  in  still  existing  groups,  or  between  them. 
That  the  extinct  forms  of  life  help  to  fill  up  the  in- 
tervals between  existing  genera,  families,  and  orders, 
is  certainly  true;  but  as  this  statement  has  often  been 
ignored  or  even  denied,  it  may  be  well  to  make  some 
remarks  on  this  subject,  and  to  give  some  instances. 
If  we  confine  our  attention  either  to  the  living  or  to  the 
extinct  species  of  the  same  class,  the  series  is  far  less 
perfect  than  if  we  combine  both  into  one  general  sys- 
tem. In  the  writings  of  Professor  Owen  we  continu- 
ally meet  with  the  expression  of  generalised  forms,  as 
applied  to  extinct  animals;  and  in  the  writings  of 
Agassiz,  of  prophetic  or  synthetic  types;  and  these 
terms  imply  that  such  forms  are  in  fact  intermediate  or 
connecting  links.  Another  distinguished  paleontolo- 
gist, M.  Gaudry,  has  shown  in  the  most  striking  manner 
that  many  of  the  fossil  mammals  discovered  by  him  in 
Attica  serve  to  break  down  the  intervals  between  exist- 
ing genera.  Cuvier  ranked  the  Ruminants  and  Pachy- 
derms as  two  of  the  most  distinct  orders  of  mammals: 
but  so  many  fossil  links  have  been  disentombed  that 
Owen  has  had  to  alter  the  whole  classification,  and  has 
placed  certain  pachyderms  in  the  same  sub-order  with 
ruminants;  for  example,  he  dissolves  by  gradations  the 
apparently  wide  interval  between  the  pig  and  the  camel. 
The  Ungulata  or  hoofed  quadrupeds  are  now  divided 
into  the  even-toed  or  odd-toed  divisions;  but  the  Mac- 
rauchenia  of  S.  America  connects  to  a  certain  extent 
these  two  grand  divisions.  No  one  will  deny  that  the 
Hipparion  is  intermediate  between  the  existing  horse 


108  AFFINITIES  OF  EXTINCT  SPECIES.  [CHAP.  XL 

and  certain  older  ungulate  forms.  What  a  wonderful 
connecting  link  in  the  chain  of  mammals  is  the  Typo- 
therium  from  S.  America,  as  the  name  given  to  it  by 
Professor  Gervais  expresses,  and  which  cannot  be  placed 
in  any  existing  order.  The  Sirenia  form  a  very  dis- 
tinct group  of  mammals,  and  one  of  the  most  remark- 
able peculiarities  in  the  existing  dugong  and  lamentin 
is  the  entire  absence  of  hind  limbs  without  even  a  rudi- 
ment being  left;  but  the  extinct  Halitherium  had,  ac- 
cording to  Professor  Flower,  an  ossified  thigh-bone 
"  articulated  to  a  well-defined  acetabulum  in  the  pelvis," 
and  it  thus  makes  some  approach  to  ordinary  hoofed 
quadrupeds,  to  which  the  Sirenia  are  in  other  respects 
allied.  The  cetaceans  or  whales  are  widely  different 
from  all  other  mammals,  but  the  tertiary  Zeuglodon 
and  Squalodon,  which  have  been  placed  by  some  natu- 
ralists in  an  order  by  themselves,  are  considered  by  Pro- 
fessor Huxley  to  be  undoubtedly  cetaceans,  "  and  to 
constitute  connecting  links  with  the  aquatic  carnivora." 

Even  the  wide  interval  between  birds  and  reptiles 
has  been  shown  by  the  naturalist  just  quoted  to  be 
partially  bridged  over  in  the  most  unexpected  manner, 
on  the  one  hand,  by  the  ostrich  and  extinct  Archeo- 
pteryx,  and  on  the  other  hand,  by  the  Compsognathus, 
one  of  the  Dinosaurians — that  group  which  includes 
the  most  gigantic  of  all  terrestrial  reptiles.  Turning  to 
the  Invertebrata,  Barrande  asserts,  and  a  higher  author- 
ity could  not  be  named,  that  he  is  every  day  taught  that, 
although  palaeozoic  animals  can  certainly  be  classed 
under  existing  groups,  yet  that  at  this  ancient  period 
the  groups  were  not  so  distinctly  separated  from  each 
other  as  they  now  are. 

Some  writers  have  objected  to  any  extinct  species, 


CHAP.  XL]  AFFINITIES  OF  EXTINCT  SPECIES.  109 

or  group  of  species,  being  considered  as  intermediate 
between  any  two  living  species,  or  groups  of  species. 
If  by  this  term  ifc  is  meant  that  an  extinct  form  is  di- 
rectly intermediate  in  all  its  characters  between  two 
living  forms  or  groups,  the  objection  is  probably  valid. 
But  in  a  natural  classification  many  fossil  species  cer- 
tainly stand  between  living  species,  and  some  extinct 
genera  between  living  genera,  even  between  genera  be- 
longing to  distinct  families.  The  most  common  case, 
especially  with  respect  to  very  distinct  groups,  such  as 
fish  and  reptiles,  seems  to  be,  that,  supposing  them  to  be 
distinguished  at  the  present  day  by  a  score  of  charac- 
ters, the  ancient  members  are  separated  by  a  somewhat 
lesser  number  of  characters;  so  that  the  two  groups 
formerly  made  a  somewhat  nearer  approach  to  each 
other  than  they  now  do. 

It  is  a  common  belief  that  the  more  ancient  a  form 
is,  by  so  much  the  more  it  tends  to  connect  by  some  of 
its  characters  groups  now  widely  separated  from  each 
other.  This  remark  no  doubt  must  be  restricted  to 
those  groups  which  have  undergone  much  change  in 
the  course  of  geological  ages;  and  it  would  be  difficult 
to  prove  the  truth  of  the  proposition,  for  every  now  and 
then  even  a  living  animal,  as  the  Lepidosiren,  is  dis- 
covered having  affinities  directed  towards  very  distinct 
groups.  Yet  if  we  compare  the  older  Eeptiles  and 
Batrachians,  the  older  Fish,  the  older  Cephalopods,  and 
the  eocene  Mammals,  with  the  more  recent  members  of 
the  same  classes,  we  must  admit  that  there  is  truth  in 
the  remark. 

Let  us  see  how  far  these  several  facts  and  inferences 
accord  with  the  theory  of  descent  with  modification. 
As  the  subject  is  somewhat  complex,  I  must  request 


HO  AFFINITIES  OF  EXTINCT  SPECIES.  [CHAP.  XL 

the  reader  to  turn  to  the  diagram  in  the  fourth  chapter. 
We  may  suppose  that  the  numbered  letters  in  italics 
represent  genera;  and  the  dotted  lines  diverging  from 
them  the  species  in  each  genus.  The  diagram  is  much 
too  simple,  too  few  genera  and  too  few  species  be- 
ing given,  but  this  is  unimportant  for  us.  The  hori- 
zontal lines  may  represent  successive  geological  forma- 
tions, and  all  the  forms  beneath  the  uppermost  line  may 
be  considered  as  extinct.  The  three  existing  genera  a14, 
?14>  P14>  will  form  a  small  family;  614  and  /14  a  closely 
allied  family  or  sub-family;  and  o14,  <?14,  ra14,  a  third 
family.  These  three  families,  together  with  the  many 
extinct  genera  on  the  several  lines  of  descent  diverging 
from  the  parent-form  (A)  will  form  an  order,  for  all 
will  have  inherited  something  in  common  from  their 
ancient  progenitor.  On  the  principle  of  the  continued 
tendency  to  divergence  of  character,  which  was  formerly 
illustrated  by  this  diagram,  the  more  recent  any  form 
is,  the  more  it  will  generally  differ  from  its  ancient 
progenitor.  Hence  we  can  understand  the  rule  that 
the  most  ancient  fossils  differ  most  from  existing  forms. 
We  must  not,  however,  assume  that  divergence  of  char- 
acter is  a  necessary  contingency;  it  depends  solely  on 
the  descendants  from  a  species  being  thus  enabled  to 
seize  on  many  and  different  places  in  the  economy  of 
nature.  Therefore  it  is  quite  possible,  as  we  have  seen 
in  the  case  of  some  Silurian  forms,  that  a  species  might 
go  on  being  slightly  modified  in  relation  to  its  slightly 
altered  conditions  of  life,  and  yet  retain  throughout  a 
vast  period  the  same  general  characteristics.  This  is 
represented  in  the  diagram  by  the  letter  r14. 

All  the  many  forms,  extinct  and  recent,  descended 
from  (A),  make,  as  before  remarked,  one  order;  and 


CHAP.  XL]  AFFINITIES  OF  EXTINCT  SPECIES.  m 

this  order,  from  the  continued  effects  of  extinction  and 
divergence  of  character,  has  become  divided  into  several 
sub-families  and  families,  some  of  which  are  supposed 
to  have  perished  at  different  periods,  and  some  to  have 
endured  to  the  present  day. 

By  looking  at  the  diagram  we  can  see  that  if  many 
of  the  extinct  forms  supposed  to  be  imbedded  in  the 
successive  formations,  were  discovered  at  several  points 
low  down  in  the  series,  the  three  existing  families  on 
the  uppermost  line  would  be  rendered  less  distinct  from 
each  other.  If,  for  instance,  the  genera  a1,  a5,  a10, 
f,  m3,  m°,  m9,  were  disinterred,  these  three  families 
would  be  so  closely  linked  together  that  they  probably 
would  have  to  be  united  into  one  great  family,  in  near- 
ly the  same  manner  as  has  occurred  with  ruminants 
and  certain  pachyderms.  Yet  he  who  objected  to  con- 
sider as  intermediate  the  extinct  genera,  which  thus 
link  together  the  living  genera  of  three  families,  would 
be  partly  justified,  for  they  are  intermediate,  not  direct- 
ly, but  only  by  a  long  and  circuitous  course  through 
many  widely  different  forms.  If  many  extinct  forms 
were  to  be  discovered  above  one  of  the  middle  hori- 
zontal lines  or  geological  formations — for  instance, 
above  No.  VI. — but  none  from  beneath  this  line,  then 
only  two  of  the  families  (those  on  the  left  hand,  a14,  &c., 
and  614,  &c.)  would  have  to  be  united  into  one;  and  there 
would  remain  two  families,  which  would  be  less  distinct 
from  each  other  than  they  were  before  the  discovery  of 
the  fossils.  So  again  if  the  three  families  formed  of 
eight  genera  (a14  to  m1*),  on  the  uppermost  line,  be  sup- 
posed to  differ  from  each  other  by  half-a-dozen  impor- 
tant characters,  then  the  families  which  existed  at  the 
period  marked  VI.  would  certainly  have  differed  from 


112  AFFINITIES  OF  EXTINCT  SPECIES.  [CHAP.  XL 

each  other  by  a  less  number  of  characters;  for  they 
would  at  this  early  stage  of  descent  have  diverged  in  a 
less  degree  from  their  common  progenitor.  Thus  it 
comes  that  ancient  and  extinct  genera  are  often  in  a 
greater  or  less  degree  intermediate  in  character  between 
their  modified  descendants,  or  between  their  collateral 
relations. 

Under  nature  the  process  will  be  far  more  compli- 
cated than  is  represented  in  the  diagram;  for  the  groups 
will  have  been  more  numerous;  they  will  have  en- 
dured for  extremely  unequal  lengths  of  time,  and  will 
have  been  modified  in  various  degrees.  As  we  possess 
only  the  last  volume  of  the  geological  record,  and  that 
in  a  very  broken  condition,  we  have  no  right  to  expect, 
except  in  rare  cases,  to  fill  up  the  wide  intervals  in  the 
natural  system,  and  thus  to  unite  distinct  families  or 
orders.  All  that  we  have  a  right  to  expect  is,  that  those 
groups  which  have,  within  known  geological  periods, 
undergone  much  modification,  should  in  the  older  for- 
mations make  some  slight  approach  to  each  other;  so  that 
the  older  members  should  differ  less  from  each  other  in 
some  of  their  characters  than  do  the  existing  members  of 
the  same  groups;  and  this  by  the  concurrent  evidence  of 
our  best  palaeontologists  is  frequently  the  case. 

Thus,  on  the  theory  of  descent  with  modification, 
the  main  facts  with  respect  to  the  mutual  affinities  of 
the  extinct  forms  of  life  to  each  other  and  to  living 
forms,  are  explained  in  a  satisfactory  manner.  And 
they  are  wholly  inexplicable  on  any  other  view. 

On  this  same  .theory,  it  is  evident  that  the  fauna 
during  any  one  great  period  in  the  earth's  history  will 
be  intermediate  in  general  character  between  that  which 
preceded  and  that  which  succeeded  it.  Thus  the  spe- 


CHAP.  XL]  AFFINITIES  OF  EXTINCT  SPECIES.  H3 

cies  which  lived  at  the  sixth  great  stage  of  descent  in 
the  diagram  are  the  modified  offspring  of  those  which 
lived  at  the  fifth  stage,  and  are  the  parents  of  those 
Avhich  became  still  more  modified  at  the  seventh  stage; 
hence  they  could  hardly  fail  to  be  nearly  intermediate  in 
character  between  the  forms  of  life  above  and  below. 
We  must,  however,  allow  for  the  entire  extinction  of  some 
preceding  forms,  and  in  any  one  region  for  the  immi- 
gration of  new  forms  from  other  regions,  and  for  a 
large  amount  of  modification  during  the  long  and  blank 
intervals  between  the  successive  formations.  Subject 
to  these  allowances,  the  fauna  of  each  geological  period 
undoubtedly  is  intermediate  in  character,  between  the 
preceding  and  succeeding  faunas.  I  need  give  only  one 
instance,  namely,  the  manner  in  which  the  fossils  of  the 
Devonian  system,  when  this  system  was  first  discovered, 
were  at  once  recognised  by  palaeontologists  as  inter- 
mediate in  character  between  those  of  the  overlying 
carboniferous,  and  underlying  Silurian  systems.  But 
each  fauna  is  not  necessarily  exactly  intermediate,  as 
unequal  intervals  of  time  have  elapsed  between  conse- 
cutive formations. 

It  is  no  real  objection  to  the  truth  of  the  statement 
that  the  fauna  of  each  period  as  a  whole  is  nearly  inter- 
mediate in  character  between  the  preceding  and  suc- 
ceeding faunas,  that  certain  genera  offer  exceptions  to 
the  rule.  For  instance,  the  species  of  mastodons  and 
elephants,  when  arranged  by  Dr.  Falconer  in  two  series, 
— in  the  first  place  according  to  their  mutual  affinities, 
and  in  the  second  place  according  to  their  periods  of  ex- 
istence,— do  not  accord  in  arrangement.  The  species 
extreme  in  character  are  not  the  oldest  or  the  most 
recent;  nor  are  those  which  are  intermediate  in  charac- 


114  AFFINITIES  OF  EXTINCT  SPECIES.  [CHAP.  XI. 

ter,  intermediate  in  age.  But  supposing  for  an  instant, 
in  this  and  other  such  cases,  that  the  record  of  the  first 
appearance  and  disappearance  of  the  species  was  com- 
plete, which  is  far  from  the  case,  we  b#ve  no  reason  to 
believe  that  forms  successively  produced  necessarily  en- 
dure for  corresponding  lengths  of  time.  A  very  an- 
cient form  may  occasionally  have  lasted  much  longer 
than  a  form  elsewhere  subsequently  produced,  especially 
in  the  case  of  terrestrial  productions  inhabiting  sepa- 
rated districts.  To  compare  small  things  with  great; 
if  the  principal  living  and  extinct  races  of  the  domestic 
pigeon  were  arranged  in  serial  affinity,  this  arrange- 
ment would  not  closely  accord  with  the  order  in  time 
of  their  production,  and  even  less  with  the  order  of 
their  disappearance;  for  the  parent  rock-pigeon  still 
lives;  and  many  varieties  between  the  rock-pigeon  and 
the  carrier  have  become  extinct;  and  carriers  which  are 
extreme  in  the  important  character  of  length  of  beak 
originated  earlier  than  short-beaked  tumblers,  which 
are  at  the  opposite  end  of  the  series  in  this  respect. 

Closely  connected  with  the  statement,  that  the  or- 
ganic remains  from  an  intermediate  formation  are  in 
some  degree  intermediate  in  character,  is  the  fact,  in- 
sisted on  by  all  palaeontologists,  that  fossils  from  two 
consecutive  formations  are  far  more  closely  related  to 
each  other,  than  are  the  fossils  from  two  remote  forma- 
tions. Pictet  gives  as  a  well-known  instance,  the  gen- 
eral resemblance  of  the  organic  remains  from  the  sev- 
eral stages  of  the  Chalk  formation,  though  the  species 
are  distinct  in  each  stage.  This  fact  alone,  from  its 
generality,  seems  to  have  shaken  Professor  Pictet  in  his 
belief  in  the  immutability  of  species.  He  who  is  ac- 
quainted with  the  distribution  of  existing  species  over 


CHAP.  XL]  AFFINITIES  OF  EXTINCT  SPECIES.  H5 

the  globe,  will  not  attempt  to  account  for  the  close  re- 
semblance of  distinct  species  in  closely  consecutive  for- 
mations, by  the  physical  conditions  of  the  ancient  areas 
having  remained  nearly  the  same.  Let  it  be  remembered 
that  the  forms  of  life,  at  least  those  inhabiting  the  sea, 
have  changed  almost  simultaneously  throughout  the 
world,  and  therefore  under  the  most  different  climates 
and  conditions.  Consider  the  prodigious  vicissitudes  of 
climate  during  the  pleistocene  period,  which  includes 
the  whole  glacial  epoch,  and  note  how  little  the  specific 
forms  of  the  inhabitants  of  the  sea  have  been  affected. 

On  the  theory  of  descent,  the  full  meaning  of  the 
fossil  remains  from  closely  consecutive  formations  be- 
ing closely  related,  though  ranked  as  distinct  species,  is 
obvious.  As  the  accumulation  of  each  formation  has 
often  been  interrupted,  and  as  long  blank  intervals  have 
intervened  between  successive  formations,  we  ought  not 
to  expect  to  find,  as  I  attempted  to  show  in  the  last 
chapter,  in  any  one  or  in  any  two  formations,  all  the  in- 
termediate varieties  between  the  species  which  appeared 
at  the  commencement  and  close  of  these  periods:  but 
'we  ought  to  find  after  intervals,  very  long  as  measured 
by  years,  but  only  moderately  long  as  measured  geologi- 
cally, closely  allied  forms,  or,  as  they  have  been  called 
by  some  authors,  representative  species;  and  these  as- 
suredly we  do  find.  We  find,  in  short,  such  evidence  of 
the  slow  and  scarcely  sensible  mutations  of  specific 
forms,  as  we  have  the  right  to  expect. 


116  STATE  OF  DEVELOPMENT  OF       [CHAP.  XL 

On  the  State  of  Development  of  Ancient  compared  with 
Living  Forms. 

We  have  seen  in  the  fourth  chapter  that  the  degree 
of  differentiation  and  specialisation  of  the  parts  in  or- 
ganic beings,  when  arrived  at  maturity,  is  the  best 
standard,  as  yet  suggested,  of  their  degree  of  perfection 
or  highness.  We  have  also  seen  that,  as  the  speciali- 
sation of  parts  is  an  advantage  to  each  being,  so  natural 
selection  will  tend  to  render  the  organisation  of  each 
being  more  specialised  and  perfect,  and  in  this  sense 
higher;  not  but  that  it  may  leave  many  creatures  with 
simple  and  unimproved  structures  fitted  for  simple  con- 
ditions of  life,  and  in  some  cases  will  even  degrade  or 
simplify  the  organisation,  yet  leaving  such  degraded 
beings  better  fitted  for  their  new  walks  of  life.  In 
another  and  more  general  manner,  new  species  become 
superior  to  their  predecessors;  for  they  have  to  beat  in 
the  struggle  for  life  all  the  older  forms,  with  which  they 
come  into  close  competition.  We  may  therefore  con- 
clude that  if  under  a  nearly  similar  climate  the  eocene 
inhabitants  of  the  world  could  be  put  into  competition 
with  the  existing  inhabitants,  the  former  would  be  beaten 
and  exterminated  by  the  latter,  as  would  the  secondary 
by  the  eocene,  and  the  palaeozoic  by  the  secondary  forms. 
So  that  by  this  fundamental  test  of  victory  in  the  battle 
for  life,  as  well  as  by  the  standard  of  the  specialisation 
of  organs,  modern  forms  ought,  on  the  theory  of  natu- 
ral selection,  to  stand  higher  than  ancient  forms.  Is 
this  the  case?  A  large  majority  of  palaeontologists 
would  answer  in  the  affirmative;  and  it  seems  that  this 
answer  must  be  admitted  as  true,  though  difficult  of 
proof. 


CQAP.  XL]      ANCIENT  AND  LIVING  FORMS.  H? 

It  is  no  valid  objection  to  this  conclusion,  that  cer- 
tain Brachiopods  have  been  but  slightly  modified  from 
an  extremely  remote  geological  epoch;  and  that  certain 
land  and  fresh-water  shells  have  remained  nearly  the 
same,  from  the  time  when,  as  far  as  is  known,  they 
first  appeared.  It  is  not  an  insuperable  difficulty  that 
Foraminifera  have  not,  as  insisted  on  by  Dr.  Carpenter, 
progressed  in  organisation  since  even  the  Laurentian 
epoch;  for  some  organisms  would  have  to  remain  fitted 
for  simple  conditions  of  life,  and  what  could  be  better 
fitted  for  this  end  than  these  lowly  organised  Protozoa? 
Such  objections  as  the  above  would  be  fatal  to  my  view, 
if  it  included  advance  in  organisation  as  a  necessary 
contingent.  They  would  likewise  be  fatal,  if  the  above 
Foraminifera,  for  instance,  could  be  proved  to  have 
first  come  into  existence  during  the  Laurentian  epoch, 
or  the  above  Brachiopods  during  the  Cambrian  forma- 
tion; for  in  this  case,  there  would  not  have  been  time 
sufficient  for  the  development  of  these  organisms  up  to 
the  standard  which  they  had  then  reached.  When 
advanced  up  to  any  given  point,  there  is  no  necessity, 
on  the  theory  of  natural  selection,  for  their  further 
continued  progress;  though  they  will,  during  each  suc- 
cessive age,  have  to  be  slightly  modified,  so  as  to  hold 
their  places  in  relation  to  slight  changes  in  their  con- 
ditions. The  foregoing  objections  hinge  on  the  ques- 
tion whether  we  really  know  how  old  the  world  is,  and 
at  what  period  the  various  forms  of  life  first  appeared; 
and  this  may  well  be  disputed. 

The  problem  whether  organisation  on  the  whole  has 
advanced  is  in  many  ways  excessively  intricate.  The 
geological  record,  at  all  times  imperfect,  does  not  ex- 
tend far  enough  back,  to  shew  with  unmistakeable  clear- 


118         •       STATE  OP  DEVELOPMENT  OF       [CHAP.  XI. 

ness  that  within  the  known  history  of  the  world  or- 
ganisation has  largely  advanced.  Even  at  the  present 
day,  looking  to  members  of  the  same  class,  naturalists 
are  not  unanimous  which  forms  ought  to  be  ranked  as 
highest:  thus,  some  look  at  the  selaceans  or  sharks, 
from  their  approach  in  some  important  points  of  struc- 
ture to  reptiles,  as  the  highest  fish;  others  look  at  the 
teleosteans  as  the  highest.  The  ganoids  stand  inter- 
mediate between  the  selaceans  and  teleosteans;  the  latter 
at  the  present  day  are  largely  preponderant  in  number; 
but  formerly  selaceans  and  ganoids  alone  existed;  and 
in  this  case,  according  to  the  standard  of  highness 
chosen,  so  will  it  be  said  that  fishes  have  advanced  or 
retrograded  in  organisation.  To  attempt  to  compare 
members  of  distinct  types  in  the  scale  of  highness  seems 
hopeless;  who  will  decide  whether  a  cuttle-fish  be  higher 
than  a  bee — that  insect  which  the  great  Von  Baer  be- 
lieved to  be  "  in  fact  more  highly  organised  than  a  fish, 
although  upon  another  type"?  In  the  complex  strug- 
gle for  life  it  is  quite  credible  that  crustaceans,  not 
very  high  in  their  own  class,  might  beat  cephalopods, 
the  highest  molluscs;  and  such  crustaceans,  though  not 
highly  developed,  would  stand  very  high  in  the  scale  of 
invertebrate  animals,  if  judged  by  the  most  decisive  of 
all  trials — the  law  of  battle.  Besides  these  inherent 
difficulties  in  deciding  which  forms  are  the  most  ad- 
vanced in  organisation,  we  ought  not  solely  to  compare 
the  highest  members  of  a  class  at  any  two  periods — 
though  undoubtedly  this  is  one  and  perhaps  the  most 
important  element  in  striking  a  balance — but  we  ought 
to  compare  all  the  members,  high  and  low,  at  the  two 
periods.  At  an  ancient  epoch  the  highest  and  lowest 
molluscoidal  animals,  namely,  cephalopods  and  brachio- 


CHAP.  XL]      ANCIENT  AND  LIVING  FORMS.  H9 

pods,  swarmed  in  numbers;  at  the  present  time  both 
groups  are  greatly  reduced,  whilst  others,  intermediate 
in  organisation,  have  largely  increased;  consequently 
some  naturalists  maintain  that  molluscs  were  formerly 
more  highly  developed  than  at  present;  but  a  stronger 
case  can  be  made  out  on  the  opposite  side,  by  consider- 
ing the  vast  reduction  of  brachiopods,  and  the  fact  that 
our  existing  cephalopods,  though  few  in  number,  are 
more  highly  organised  than  their  ancient  representa- 
tives. We  ought  also  to  compare  the  relative  propor- 
tional numbers  at  any  two  periods  of  the  high  and  low 
classes  throughout  the  world:  if,  for  instance,  at  the 
present  day  fifty  thousand  kinds  of  vertebrate  animals 
exist,  and  if  we  knew  that  at  some  former  period  only 
ten  thousand  kinds  existed,  we  ought  to  look  at  this  in- 
crease in  number  in  the  highest  class,  which  implies  a 
great  displacement  of  lower  forms,  as  a  decided  advance 
in  the  organisation  of  the  world.  We  thus  see  how 
hopelessly  difficult  it  is  to  compare  with  perfect  fair- 
ness under  such  extremely  complex  relations,  the  stand- 
ard of  organisation  of  the  imperfectly-known  faunas  of 
successive  periods. 

We  shall  appreciate  this  difficulty  more  clearly,  by 
looking  to  certain  existing  faunas  and  floras.  From  the 
extraordinary  manner  in  which  European  productions 
have  recently  spread  over  New  Zealand,  and  have  seized 
on  places  which  must  have  been  previously  occupied  by 
the  indigenes,  we  must  believe,  that  if  all  the  animals 
and  plants  of  Great  Britain  were  set  free  in  New  Zea- 
land, a  multitude  of  British  forms  would  in  the  course 
of  time  become  thoroughly  naturalised  there,  and  would 
exterminate  many  of  the  natives.  On  the  other  hand, 
from  the  fact  that  hardly  a  single  inhabitant  of  the 


120  STATE  OF  DEVELOPMENT  OF       [CHAP.  XI. 

southern  hemisphere  has  become  wild  in  any  part  of 
Europe,  we  may  well  doubt  whether,  if  all  the  produc- 
tions of  New  Zealand  were  set  free  in  Great  Britain,  any 
considerable  number  would  be  enabled  to  seize  on  places 
now  occupied  by  our  native  plants  and  animals.  Under 
this  point  of  view,  the  productions  of  Great  Britain 
stand  much  higher  in  the  scale  than  those  of  New  Zea- 
land. Yet  the  most  skilful  naturalist,  from  an  exami- 
nation of  the  species  of  the  two  countries,  could  not  have 
foreseen  this  result. 

Agassiz  and  several  other  highly  competent  judges 
insist  that  ancient  animals  resemble  to  a  certain  extent 
the  embryos  of  recent  animals  belonging  to  the  same 
classes;  and  that  the  geological  succession  of  extinct 
forms  is  nearly  parallel  with  the  embryological  de- 
velopment of  existing  forms.  This  view  accords  ad- 
mirably well  with  our  theory.  In  a  future  chapter  I 
shall  attempt  to  show  that  the  adult  differs  from  its 
embryo,  owing  to  variations  having  supervened  at  a  not 
early  age,  and  having  been  inherited  at  a  corresponding 
age.  This  process,  whilst  it  leaves  the  embryo  almost 
unaltered,  continually  adds,  in  the  course  of  successive 
generations,  more  and  more  difference  to  the  adult. 
Thus  the  embryo  comes  to  be  left  as  a  sort  of  picture, 
preserved  by  nature,  of  the  former  and  less  modified 
condition  of  the  species.  This  view  may  be  true,  and 
yet  may  never  be  capable  of  proof.  Seeing,  for  instance, 
that  the  oldest  known  mammals,  reptiles,  and  fishes 
strictly  belong  to  their  proper  classes,  though  some  of 
these  old  forms  are  in  a  slight  degree  less  distinct  from 
each  other  than  are  the  typical  members  of  the  same 
groups  at  the  present  day,  it  would  be  vain  to  look  for 
animals  having  the  common  embryological  character  of 


CHAP.  XL]      ANCIENT  AND  LIVING  FORMS.  121 

the  Vertebrata,  until  beds  rich  in  fossils  are  discovered 
far  beneath  the  lowest  Cambrian  strata — a  discovery  of 
which  the  chance  is  small. 

On  the  Succession  of  the  same  Types  within  the  same 
Areas,  during  the  later  Tertiary  periods. 

Mr.  Clift  many  years  ago  showed  that  the  fossil 
mammals  from  the  Australian  caves  were  closely  allied 
to  the  living  marsupials  of  that  continent.  In  South 
America  a  similar  relationship  is  manifest,  even  to  an 
uneducated  eye,  in  the  gigantic  pieces  of  armour,  like 
those  of  the  armadillo,  found  in  several  parts  of  La 
Plata;  and  Professor  Owen  has  shown  in  the  most  strik- 
ing manner  that  most  of  the  fossil  mammals,  buried 
there  in  such  numbers,  are  related  to  South  American 
types.  This  relationship  is  even  more  clearly  seen  in 
the  wonderful  collection  of  fossil  bones  made  by  MM. 
Lund  and  Clausen  in  the  caves  of  Brazil.  I  was  so 
much  impressed  with  these  facts  that  I  strongly  insisted, 
in  1839  and  1845,  on  this  "  law  of  the  succession  of 
types," — on  "this  wonderful  relationship  in  the  same 
continent  between  the  dead  and  the  living."  Professor 
Owen  has  subsequently  extended  the  same  generalisation 
to  the  mammals  of  the  Old  World.  We  see  the  same 
law  in  this  author's  restorations  of  the  extinct  and 
gigantic  birds  of  New  Zealand.  We  see  it  also  in  the 
birds  of  the  caves  of  Brazil.  Mr.  Woodward  has  shown 
that  the  same  law  holds  good  with  sea-shells,  but,  from 
the  wide  distribution  of  most  molluscs,  it  is  not  well 
displayed  by  them.  Other  cases  could  be  added,  as  the 
relation  between  the  extinct  and  living  land-shells  of 
Madeira;  and  between  the  extinct  and  living  brackish 
water-shells  of  the  Aralo-Caspian  Sea. 


122  SUCCESSION  OF  THE  [CHAP.  XI. 

Now  what  does  this  remarkable  law  of  the  succession 
of  the  same  types  within  the  same  areas  mean?  He 
would  be  a  bold  man  who,  after  comparing  the  present 
climate  of  Australia  and  of  parts  of  South  America, 
under  the  same  latitude,  would  attempt  to  account,  on 
the  one  hand  through  dissimilar  physical  conditions,  for 
the  dissimilarity  of  the  inhabitants  of  these  two  con- 
tinents; and,  on  the  other  hand  through  similarity  of 
conditions,  for  the  uniformity  of  the  same  types  in  each 
continent  during  the  later  tertiary  periods.  Nor  can  it 
be  pretended  that  it  is  an  immutable  law  that  marsupials 
should  have  been  chiefly  or  solely  produced  in  Australia; 
or  that 'Edentata  and  other  American  types  should  have 
been  solely  produced  in  South  America.  For  we  know 
that  Europe  in  ancient  times  was  peopled  by  numerous 
marsupials;  and  I  have  shown  in  the  publications  above 
alluded  to,  that  in  America  the  law  of  distribution  of 
terrestrial  mammals  was  formerly  different  from  what  it 
now  is.  North  America  formerly  partook  strongly  of 
the  present  character  of  the  southern  half  of  the  con- 
tinent; and  the  southern  half  was  formerly  more  closely 
allied,  than  it  is  at  present,  to  the  northern  half.  In  a 
similar  manner  we  know,  from  Falconer  and  Cautley's 
discoveries,  that  Northern  India  was  formerly  more 
closely  related  in  its  mammals  to  Africa  than  it  is  at  the 
present  time.  Analogous  facts  could  be  given  in  rela- 
tion to  the  distribution  of  marine  animals. 

On  the  theory  of  descent  with  modification,  the 
great  law  of  the  long  enduring,  but  not  immutable,  suc- 
cession of  the  same  types  within  the  same  areas,  is  at 
once  explained;  for  the  inhabitants  of  each  quarter  of 
the  world  will  obviously  tend  to  leave  in  that  quarter, 
during  the  next  succeeding  period  of  time,  closely  allied 


CHAP.  XL]  SAME  TYPES  IN  THE  SAME  AREAS.  123 

though  in  some  degree  modified  descendants.  If  the 
inhabitants  of  one  continent  formerly  differed  greatly 
from  those  of  another  continent,  so  will  their  modified 
descendants  still  differ  in  nearly  the  same  manner  and 
degree.  But  after  very  long  intervals  of  time,  and 
after  great  geographical  changes,  permitting  much  in- 
termigration,  the  feebler  will  yield  to  the  more  domi- 
nant forms,  and  there  will  be  nothing  immutable  in  the 
distribution  of  organic  beings. 

It  may  be  asked  in  ridicule,  whether  I  suppose  thafr 
the  megatherium  and  other  allied  huge  monsters,  which 
formerly  lived  in  South  America,  have  left  behind  them 
the  sloth,  armadillo,  and  anteater,  as  their  degenerate 
descendants.  This  cannot  for  an  instant  be  admitted. 
These  huge  animals  have  become  wholly  extinct,  and 
have  left  no  progeny.  But  in  the  caves  of  Brazil,  there 
are  many  extinct  species  which  are  closely  allied  in  size 
and  in  all  other  characters  to  the  species  still  living  in 
South  America;  and  some  of  these  fossils  may  have  been 
the  actual  progenitors  of  the  living  species.  It  must 
not  be  forgotten  that,  on  our  theory,  all  the  species  of  the 
same  genus  are  the  descendants  of  some  one  species;  so 
that,  if  six  genera,  each  having  eight  species,  be  found  in 
one  geological  formation,  and  in  a  succeeding  forma- 
tion there  be  six  other  allied  or  representative  genera 
each  with  the  same  number  of  species,  then  we  may  con- 
clude that  generally  only  one  species  of  each  of  the  older 
genera  has  left  modified  descendants,  which  constitute 
the  new  geneja  containing  the  several  species;  the  other 
seven  species  of  each  old  genus  having  died  out  and  left 
no  progeny.  Or,  and  this  will  be  a  far  commoner  case, 
two  or  three  species  in  two  or  three  alone  of  the  six 
older  genera  will  be  the  parents  of  the  new  genera:  the 


124:  SUMMARY  OF  THE  [CHAP.  XI. 

other  species  and  the  other  old  genera  having  become 
utterly  extinct.  In  failing  orders,  with  the  genera  and 
species  decreasing  in  numbers  as  is  the  case  with  the 
Edentata  of  South  America,  still  fewer  genera  and  spe- 
cies will  leave  modified  blood-descendants. 


Summary  of  the  preceding  and  present  Chapters. 

I  have  attempted  to  show  that  the  geological  record 
is  extremely  imperfect;  that  only  a  small  portion  of  the 
globe  has  been  geologically  explored  with  care;  that 
only  certain  classes  of  organic  beings  have  been  largely 
preserved  in  a  fossil  state;  that  the  number  both  of 
specimens  and  of  species,  preserved  in  our  museums,  is 
absolutely  as  nothing  compared  with  the  number  of 
generations  which  must  have  passed  away  even  during  a 
single  formation;  that,  owing  to  subsidence  being  al- 
most necessary  for  the  accumulation  of  deposits  rich  in 
fossil  species  of  many  kinds,  and  thick  enough  to  outlast 
future  degradation,  great  intervals  of  time  must  have 
elapsed  between  most  of  our  successive  formations;  that 
there  has  probably  been  more  extinction  during  the 
periods  of  subsidence,  and  more  variation  during  the 
periods  of  elevation,  and  during  the  latter  the  record 
will  have  been  less  perfectly  kept;  that  each  single  for- 
mation has  not  been  continuously  deposited;  that  the 
duration  of  each  formation  is  probably  short  compared 
with  the  average  duration  of  specific  forms;  that  mi- 
gration has  played  an  important  part  in -the  first  ap- 
pearance of  new  forms  in  any  one  area  and  formation; 
that  widely  ranging  species  are  those  which  have  varied 
most  frequently,  and  have  oftenest  given  rise  to  new 
species;  that  varieties  have  at  first  been  local;  and  lastly, 


CHAP.  XL]  PRECEDING  AND  PRESENT  CHAPTERS.     125 

although  each  species  must  have  passed  through  numer- 
ous transitional  stages,  it  is  probable  that  the  periods, 
during  which  each  underwent  modification,  though 
many  and  long  as  measured  by  years,  have  been  short 
in  comparison  with  the  periods  during  which  each  re- 
mained in  an  unchanged  condition.  These  causes, 
taken  conjointly,  will  to  a  large  extent  explain  why — 
though  we  do  find  many  links — we  do  not  find  inter- 
minable varieties,  connecting  together  all  extinct  and 
existing  forms  by  the  finest  graduated  steps.  It  should 
also  be  constantly  borne  in  mind  that  any  linking  va- 
riety between  two  forms,  which  might  be  found,  would 
be  ranked,  unless  the  whole  chain  could  be  perfectly 
restored,  as  a  new  and  distinct  species;  for  it  is  not  pre- 
tended that  we  have  any  sure  criterion  by  which  species 
and  varieties  can  be  discriminated. 

He  who  rejects  this  view  of  the  imperfection  of  the 
geological  record,  will  rightly  reject  the  whole  theory. 
For  he  may  ask  in  vain  where  are  the  numberless  tran- 
sitional links  which  must  formerly  have  connected  the 
closely  allied  or  representative  species,  found  in  the 
successive  stages  of  the  same  great  formation?  He 
may  disbelieve  in  the  immense  intervals  of  time  which 
must  have  elapsed  between  our  consecutive  formations; 
he  may  overlook  how  important  a  part  migration  has 
played,  when  the  formations  of  any  one  great  region, 
as  those  of  Europe,  are  considered;  he  may  urge  the 
apparent,  but  often  falsely  apparent,  sudden  coming  in 
of  whole  groups  of  species.  He  may  ask  where  are  the 
remains  of  those  infinitely  numerous  organisms  which 
must  have  existed  long  before  the  Cambrian  system 
was  deposited?  We  now  know  that  at  least  one  animal 
did  then  exist;  but  I  can  answer  this  last  question  only 


126  SUMMARY  OF  THE  [CHAP.  XI. 

by  supposing  that  where  our  oceans  now  extend  they 
have  extended  for  an  enormous  period,  and  where  our 
oscillating  continents  now  stand  they  have  stood  since 
the  commencement  of  the  Cambrian  system;  but  that, 
long  before  that  epoch,  the  world  presented  a  widely 
different  aspect;  and  that  the  older  continents  formed 
of  formations  older  than  any  known  to  us,  exist  now 
only  as  remnants  in  a  metamorphosed  condition,  or  lie 
still  buried  under  the  ocean. 

Passing  from  these  difficulties,  the  other  great  lead- 
ing facts  in  palaeontology  agree  admirably  with  the 
theory  of  descent  with  modification  through  variation 
and  natural  selection.  We  can  thus  understand  how 
it  is  that  new  species  come  in  slowly  and  successively; 
how  species  of  different  classes  do  not  necessarily  change 
together,  or  at  the  same  rate,  or  in  the  same  degree; 
yet  in  the  long  run  that  all  undergo  modification  to 
some  extent.  The  extinction  of  old  forms  is  the  almost 
inevitable  consequence  of  the  production  of  new  forms. 
We  can  understand  why,  when  a  species  has  once  dis- 
appeared, it  never  reappears.  Groups  of  species  in- 
crease in  numbers  slowly,  and  endure  for  unequal 
periods  of  time;  for  the  process  of  modification  is  neces- 
sarily slow,  and  depends  on  many  complex  contingen- 
cies. The  dominant  species  belonging  to  large  and 
dominant  groups  tend  to  leave  many  modified  descend- 
ants, which  form  new  sub-groups  and  groups.  As  these 
are  formed,  the  species  of  the  less  vigorous  groups,  from 
their  inferiority  inherited  from  a  common  progenitor, 
tend  to  become  extinct  together,  and  to  leave  no  modi- 
fied offspring  on  the  face  of  the  earth.  But  the  utter 
extinction  of  a  whole  group  of  species  has  sometimes 
been  a  slow  process,  from  the  survival  of  a  few  descend- 


CHAP.  XL]  PRECEDING  AND  PRESENT  CHAPTERS.     127 

ants,  lingering  in  protected  and  isolated  situations. 
When  a  group  has  once  wholly  disappeared,  it  does  not 
reappear;  for  the  link  of  generation  has  been  broken. 

We  can  understand  how  it  is  that  dominant  forms 
which  spread  widely  and  yield  the  greatest  number  of 
varieties  tend  to  people  the  world  with  allied,  but  modi- 
fied, descendants;  and  these  will  generally  succeed  in 
displacing  the  groups  which  are  their  inferiors  in  the 
struggle  for  existence.  Hence,  after  long  intervals  of 
time,  the  productions  of  the  world  appear  to  have 
changed  simultaneously. 

We  can  understand  how  it  is  that  all  the  forms  of 
life,  ancient  and  recent,  make  together  a  few  grand 
classes.  We  can  understand,  from  the  continued  ten- 
dency to  divergence  of  character,  why  the  more  ancient 
a  form  is,  the  more  it  generally  differs  from  those  now 
living;  why  ancient  and  extinct  forms  often  tend  to 
fill  up  gaps  between  existing  forms,  sometimes  blending 
two.  groups,  previously  classed  as  distinct,  into  one;  but 
more  commonly  bringing  them  only  a  little  closer  to- 
gether. The  more  ancient  a  form  is,  the  more  often 
it  stands  in  some  degree  intermediate  between  groups 
now  distinct;  for  the  more  ancient  a  form  is,  the  more 
nearly  it  will  be  related  to,  and  consequently  resemble, 
the  common  progenitor  of  groups,  since  become  widely 
divergent.  Extinct  forms  are  seldom  directly  inter- 
mediate between  existing  forms;  but  are  intermediate 
only  by  a  long  and  circuitous  course  through  other  ex- 
tinct and  different  forms.  We  can  clearly  see  why  the 
organic  remains  of  closely  consecutive  formations  are 
closely  allied;  for  they  are  closely  linked  together  by 
generation.  We  can  clearly  see  why  the  remains  of  an 
intermediate  formation  are  intermediate  in  character. 


128  SUMMARY  OP  CHAPTERS.  [CHAP.  XI. 

The  inhabitants  of  the  world  at  each  successive 
period  in  its  history  have  beaten  their  predecessors  in 
the  race  for  life,  and  are,  in  so  far,  higher  in  the  scale, 
and  their  structure  has  generally  become  more  special- 
ised; and  this  may  account  for  the  common  belief  held 
by  so  many  palaeontologists,  that  organisation  on  the 
whole  has  progressed.  Extinct  and  ancient  animals  re- 
semble to  a  certain  extent  the  embryos  of  the  more  re- 
cent animals  belonging  to  the  same  classes,  and  this 
wonderful  fact  receives  a  simple  explanation  according 
to  our  views.  The  succession  of  the  same  types  of 
structure  within  the  same  areas  during  the  later  geologi- 
cal periods  ceases  to  be  mysterious,  and  is  intelligible 
on  the  principle  of  inheritance. 

If  then  the  geological  record  be  as  imperfect  as  many 
believe,  and  it  may  at  least  be  asserted  that  the  record 
cannot  be  proved  to  be  much  more  perfect,  the  main 
objections  to  the  theory  of  natural  selection  are  greatly 
diminished  or  disappear.  On  the  other  hand,  all  the 
chief  laws  of  palaeontology  plainly  proclaim,  as  it  seems 
to  me,  that  species  have  been  produced  by  ordinary  gen- 
eration: old  forms  having  been  supplanted  by  new  and 
improved  forms  of  life,  the  products  of  Variation  and 
the  Survival  of  the -Fittest. 


CHAP.  XII.]     GEOGRAPHICAL  DISTRIBUTION.  129 


CHAPTER   XII. 

GEOGBAPHICAL   DISTRIBUTION. 

Present  distribution  cannot  be  accounted  for  by  differences  in 
physical  conditions — Importance  of  barriers — Affinity  of  the 
productions  of  the  same  continent— Centres  of  creation— Means 
of  dispersal  by  changes  of  climate  and  of  the  level  of  the  land, 
and  by  occasional  means — Dispersal  during  the  Glacial  period 
—Alternate  Glacial  periods  in  the  North  and  South. 

IN  considering  the  distribution  of  organic  beings 
over  the  face  of  the  globe,  the  first  great  fact  which 
strikes  us  is,  that  neither  the  similarity  nor  the  dissimi- 
larity of  the  inhabitants  of  various  regions  can  be  wholly 
accounted  for  by  climatal  and  other  physical  conditions. 
Of  late,  almost  every  author  who  has  studied  the  subject 
has  come  to  this  conclusion.  The  case  of  America 
alone  would  almost  suffice  to  prove  its  truth;  for  if  we 
exclude  the  arctic  and  northern  temperate  parts,  all 
authors  agree  that  one  of  the  most  fundamental  divi- 
sions in  geographical  distribution  is  that  between  the 
New  and  Old  Worlds;  yet  if  we  travel  over  the  vast 
American  continent,  from  the  central  parts  of  the 
United  States  to  its  extreme  southern  point,  we  meet 
with  the  most  diversified  conditions;  humid  districts, 
arid  deserts,  lofty  mountains,  grassy  plains,  forests, 
marshes,  lakes,  and  great  rivers,  under  almost  every 
temperature.  There  is  hardly  a  climate  or  condition 
in  the  Old  World  which  cannot  be  paralleled  in  the  New 


130  GEOGRAPHICAL  DISTRIBUTION.    [CHAP.  XII. 

— at  least  as  closely  as  the  same  species  generally  re- 
quire. No  doubt  small  areas  can  be  pointed  out  in  the 
Old  World  hotter  than  any  in  the  New  World;  but 
these  are  not  inhabited  by  a  fauna  different  from  that  of 
the  surrounding  districts;  for  it  is  rare  to  find  a  group 
of  organisms  confined  to  a  small  area,  of  which  the  con- 
ditions are  peculiar  in  only  a  slight  degree.  Notwith- 
standing this  general  parallelism  in  the  conditions  of 
the  Old  and  New  Worlds,  how  widely  different  are  their 
living  productions! 

In  the  southern  hemisphere,  if  we  compare  large 
tracts  of  land  in  Australia,  South  Africa,  and  western 
South  America,  between  latitudes  25°  and  35°,  we  shall 
find  parts  extremely  similar  in  all  their  conditions,  yet 
it  would  not  be  possible  to  point  out  three  faunas  and 
floras  more  utterly  dissimikr.  Or,  again,  we  may  com- 
pare the  productions  of  South  America  south  of  lat.  35° 
with  those  north  of  25°,  which  consequently  are  sepa- 
rated by  a  space  of  ten  degrees  of  latitude,  and  are  ex- 
posed to  considerably  different  conditions;  yet  they  are 
incomparably  more  closely  related  to  each  other  than 
they  are  to  the  productions  of  Australia  or  Africa  under 
nearly  the  same  climate.  Analogous  facts  could  be 
given  with  respect  to  the  inhabitants  of  the  sea. 

A  second  great  fact  which  strikes  us  in  our  general 
review  is,  that  barriers  of  any  kind,  or  obstacles  to  free 
migration,  are  related  in  a  close  and  important  manner 
to  the  differences  between  the  productions  of  various 
regions.  We  see  this  in  the  great  difference  in  nearly 
all  the  terrestrial  productions  of  the  New  and  Old 
Worlds,  excepting  in  the  northern  parts,  where  the  land 
almost  joins,  and  where,  under  a  slightly  different  cli- 
mate, there  might  have  been  free  migration  for  the 


CHAP.  XII].    GEOGRAPHICAL  DISTRIBUTION.  131 

northern  temperate  forms,  as  there  now  is  for  the  strict- 
ly arctic  productions.  We  see  the  same  fact  in  the 
great  difference  between  the  inhabitants  of  Australia, 
Africa,  and  South  America  under  the  same  latitude; 
for  these  countries  are  almost  as  much  isolated  from 
each  other  as  is  possible.  On  each  continent,  also,  we 
see  the  same  fact;  for  on  the  opposite  sides  of  lofty 
and  continuous  mountain-ranges,  of  great  deserts  and 
even  of  large  rivers,  we  find  different  productions; 
though  as  mountain-chains,  deserts,  &c.,  are  not  as 
impassable,  or  likely  to  have  endured  so  long,  as  the 
oceans  separating  continents,  the  differences  are  very 
inferior  in  degree  to  those  characteristic  of  distinct  con- 
tinents. 

Turning  to  the  sea,  we  find  the  same  law.  The 
marine  inhabitants  of  the  eastern  and  western  shores 
of  South  America  are  very  distinct,  with  extremely  few 
shells,  Crustacea,  or  echinodermata  in  common;  but  Dr. 
Giinther  has  recently  shown  that  about  thirty  per  cent, 
of  the  fishes  are  the  same  on  the  opposite  sides  of  the 
isthmus  of  Panama;  and  this  fact  has  led  naturalists 
to  believe  that  the  isthmus  was  formerly  open.  West- 
ward of  the  shores  of  America,  a  wide  space  of  open 
ocean  extends,  with  not  an  island  as  a  halting-place  for 
emigrants;  here  we  have  a  barrier  of  another  kind,  and 
as  soon  as  this  is  passed  we  meet  in  the  eastern  islands 
of  the  Pacific  with  another  and  totally  distinct  fauna. 
So  that  three  marine  faunas  range  far  northward  and 
southward  in  parallel  lines  not  far  from  each  other, 
under  corresponding  climates;  but  from  being  sepa- 
rated from  each  other  by  impassable  barriers,  either  of 
land  or  open  sea,  they  are  almost  wholly  distinct.  On 
llic  other  hand,  proceeding  still  farther  westward  from 


132  GEOGRAPHICAL  DISTRIBUTION.   [CHAP.  XII. 

the  eastern  islands  of  the  tropical  parts  of  the  Pacific, 
we  encounter  no  impassable  barriers,  and  we  have  in- 
numerable islands  as  halting-places,  or  continuous 
coasts,  until,  after  travelling  over  a  hemisphere,  we 
come  to  the  shores  of  Africa;  and  over  this  vast  space 
we  meet  with  no  well-defined  and  distinct  marine  fau- 
nas. Although  so  few  marine  animals  are  common 
to  the  above-named  three  approximate  faunas  of  East- 
ern and  Western  America  and  the  Eastern  Pacific  is- 
lands, yet  many  fishes  range  from  the  Pacific  into  the 
Indian  Ocean,  and  many  shells  are  common  to  the  east- 
ern islands  of  the  Pacific  and  the  eastern  shores  of 
Africa  on  almost  exactly  opposite  meridians  of  longi- 
tude. 

A  third  great  fact,  partly  included  in  the  foregoing 
statement,  is  the  affinity  of  the  productions  of  the  same 
continent  or  of  the  same  sea,  though  the  species  them- 
selves are  distinct  at  different  points  and  stations.  It 
is  a  law  of  the  widest  generality,  and  every  continent 
offers  innumerable  instances.  Nevertheless  the  natural- 
ist, in  travelling,  for  instance,  from  north  to  south, 
never  fails  to  be  struck  by  the  manner  in  which  suc- 
cessive groups  of  beings,  specifically  distinct,  though 
nearly  related,  replace  each  other.  He  hears  from  close- 
ly allied,  yet  distinct  kinds  of  birds,  notes  nearly  similar, 
and  sees  their  nests  similarly  constructed,  but  not  quite 
alike,  with  eggs  coloured  in  nearly  the  same  manner. 
The  plains  near  the  Straits  of  Magellan  are  inhabited 
by  one  species  of  Rhea  (American  ostrich)  and  north- 
ward the  plains  of  La  Plata  by  another  species  of  the 
same  genus;  and  not  by  a  true  ostrich  or  emu,  like  those 
inhabiting  Africa  and  Australia  under  the  same  lati- 
tude. On  these  same  plains  of  La  Plata  we  see  the 


CHAP.  XII.]  GEOGRAPHICAL  DISTRIBUTION.  133 

agouti  and  bizcacha,  animals  having  nearly  the  same 
habits  as  our  hares  and  rabbits,  and  belonging  to  the 
same  order  of  Kodents,  but  they  plainly  display  an 
American  type  of  structure.  We  ascend  the  lofty  peaks 
of  the  Cordillera,  and  we  find  an  alpine  species  of  bizca- 
cha; we  look  to  the  waters,  and  we  do  not  find  the 
beaver  or  musk-rat,  but  the  coypu  and  capybara,  ro- 
dents of  the  S.  American  type.  Innumerable  other 
instances  could  be  given.  If  we  look  to  the  islands  of! 
the  American  shore,  however  much  they  may  differ  in 
geological  structure,  the  inhabitants  are  essentially 
American,  though  they  may  be  all  peculiar  species.  We 
may  look  back  to  past  ages,  as  shown  in  the  last  chapter, 
and  we  find  American  types  then  prevailing  on  the 
American  continent  and  in  the  American  seas.  We 
see  in  these  facts  some  deep  organic  bond,  through- 
out space  and  time,  over  tbe  same  areas  of  land  and 
water,  independently  of  physical  conditions.  The  natu- 
ralist must  be  dull  who  is  not  led  to  enquire  what  this 
bond  is. 

The  bond  is  simply  inheritance,  that  cause  which 
alone,  as  far  as  we  positively  know,  produces  organisms 
quite  like  each  other,  or,  as  we  see  in  the  case  of  varie- 
ties, nearly  alike.  The  dissimilarity  of  the  inhabitants 
of  different  regions  may  be  attributed  to  modification 
through  variation  and  natural  selection,  and  probably 
in  a  subordinate  degree  to  the  definite  influence  of  dif- 
ferent physical  conditions.  The  degrees  of  dissimilar- 
ity will  depend  on  the  migration  of  the  more  dominant 
forms  of  life  from  one  region  into  another  having  been 
more  or  less  effectually  prevented,  at  periods  more  or 
less  remote; — on  the  nature  and  number  of  the  former 
immigrants; — and  on  the  action  of  the  inhabitants  on 


13±  GEOGRAPHrCAL  DISTRIBUTION.   [CHAP.  XIL. 

each  other  in  leading  to  the  preservation  of  different 
modifications;  the  relation  of  organism  to  organism  in 
the  struggle  for  life  being,  as  I  have  already  often  re- 
marked, the  most  important  of  all  relations.  Thus  the 
high  importance  of  barriers  comes  into  play  by  check- 
ing migration;  as  does  time  for  the  slow  process  of 
modification  through  natural  selection.  Widely-rang- 
ing species,  abounding  in  individuals,  which  have  al- 
ready triumphed  over  many  competitors  in  their  own 
widely-extended  homes,  will  have  the  best  chance  of 
seizing  on  new  places,  when  they  spread  into  new  coun- 
tries. In  their  new  homes  they  will  be  exposed  to  new 
conditions,  and  will  frequently  undergo  further  modi- 
fication and  improvement;  and  thus  they  will  become  still 
further  victorious,  and  will  produce  groups  of  modified 
descendants.  On  this  principle  of  inheritance  with 
modification  we  can  understand  how  it  is  that  sec- 
tions of  genera,  whole  genera,  and  even  families,  are 
confined  to  the  same  areas,  as  is  so  commonly  and  notori- 
ously the  case. 

There  is  no  evidence,  as  was  remarked  in  the  last 
chapter,  of  the  existence  of  any  law  of  necessary  de- 
velopment. As  the  variability  of  each  species  is  an 
independent  property,  and  will  be  taken  advantage  of 
by  natural  selection,  only  so  far  as  it  profits  each  in- 
dividual in  its  complex  struggle  for  life,  so  the  amount 
of  modification  in  different  species  will  be  no  uniform 
quantity.  If  a  number  of  species,  after  having  long 
competed  with  each  other  in  their  old  home,  were  to 
migrate  in  a  body  into  a  new  and  afterwards  isolated 
country,  they  would  be  little  liable  to  modification;  for 
neither  migration  nor  isolation  in  themselves  effect  any- 
thing. These  principles  come  into  play  only  by  bring- 


CHAP.  XII.]  SINGLE  CENTRES  OF  CREATION.  135 

ing  organisms  into  new  relations  with  each  other  and  in 
a  lesser  degree  with  the  surrounding  physical  condi- 
tions. As  we  have  seen  in  the  last  chapter  that  some 
forms  have  retained  nearly  the  same  character  from  an 
enormously  remote  geological  period,  so  certain  species 
have  migrated  over  vast  spaces,  and  have  not  become 
greatly  or  at  all  modified. 

According  to  these  views,  it  is  obvious  that  the  sev- 
eral species  of  the  same  genus,  though  inhabiting  the 
most  distant  quarters  of  the  world,  must  originally  have 
proceeded  from  the  same  source,  as  they  are  descended 
from  the  same  progenitor.  In  the  case  of  those  species 
which  have  undergone  during  whole  geological  periods 
little  modification,  there  is  not  much  difficulty  in  be- 
lieving that  they  have  migrated  from  the  same  region; 
for  during  the  vast  geographical  and  climatal  changes 
which  have  supervened  since  ancient  times,  almost  any 
amount  of  migration  is  possible.  But  in  many  other 
cases,  in  which  we  have  reason  to  believe  that  the  spe- 
cies of  a  genus  have  been  produced  within  comparative- 
ly recent  times,  there  is  great  difficulty  on  this  head. 
It  is  also  obvious  that  the  individuals  of  the  same  spe- 
cies, though  now  inhabiting  distant  and  isolated  regions, 
must  have  proceeded  from  one  spot,  where  their  parents 
were  first  produced:  for,  as  has  been  explained,  it  is 
incredible  that  individuals  identically  the  same  should 
have  been  produced  from  parents  specifically  dis- 
tinct. 

Single  Centres  of  supposed  Creation. — We  are  thus 
brought  to  the  question  which  has  been  largely  dis- 
cussed by  naturalists,  namely,  whether  species  have 
been  created  at  one  or  more  points  of  the  earth's  sur- 
face. Undoubtedly  there  are  many  cases  of  extreme 


136  SINGLE  CENTRES  OF  CREATION.  [CHAP.  XII. 

difficulty  in  understanding  how  the  same  species  could 
possibly  have  migrated  from  some  one  point  to  the  sev- 
eral distant  and  isolated  points,  where  now  found. 
Nevertheless  the  simplicity  of  the  view  that  each  spe- 
cies was  first  produced  within  a  single  region  captivates 
the  mind.  He  who  rejects  it,  rejects  the  vera  causa  of 
ordinary  generation  with  subsequent  migration,  and 
calls  in  the  agency  of  a  miracle.  It  is  universally  ad- 
mitted, that  in  most  cases  the  area  inhabited  by  a  spe- 
cies is  continuous;  and  that  when  a  plant  or  animal 
inhabits  two  points  so  distant  from  each  other,  or  with 
an  interval  of  such  a  nature,  that  the  space  could  not 
have  been  easily  passed  over  by  migration,  the  fact  is 
given  as  something  remarkable  and  exceptional.  The 
incapacity  of  migrating  across  a  wide  sea  is  more  clear 
in  the  case  of  terrestrial  mammals  than  perhaps  with 
any  other  organic  beings;  and,  accordingly,  we  find  no 
inexplicable  instances  of  the  same  mammals  inhabit- 
ing distant  points  of  the  world.  No  geologist  feels  any 
difficulty  in  Great  Britain  possessing  the  same  quad- 
rupeds with  the  rest  of  Europe,  for  they  were  no  doubt 
once  united.  But  if  the  same  species  can  be  produced 
at  two  separate  points,  why  do  we  not  find  a  single  mam- 
mal common  to  Europe  and  Australia  or  South  Amer- 
ica? The  conditions  of  life  are  nearly  the  same,  so  that 
a  multitude  of  European  animals  and  plants  have  be- 
come naturalised  in  America  and  Australia;  and  some 
of  the  aboriginal  plants  are  identically  the  same 
at  these  distant  points  of  the  northern  and  southern 
hemispheres?  The  answer,  as  I  believe,  is,  that  mam- 
mals have  not  been  able  to  migrate,  whereas  some  plants, 
from  their  varied  means  of  dispersal,  have  migrated 
across  the  wide  and  broken  interspaces.  The  great 


CHAP.  XII.]  SINGLE  CENTRES  OP  CREATION.  137 

and  striking  influence  of  barriers  of  all  kinds,  is  intelli- 
gible only  on  the  view  that  the  great  majority  of  species 
have  been  produced  on  one  side,  and  have  not  been  able 
to  migrate  to  the  opposite  side.  Some  few  families, 
many  sub-families,  very  many  genera,  and  a  still  greater 
number  of  sections  of  genera,  are  confined  to  a  single 
region;  and  it  has  been  observed  by  several  naturalists 
that  the  most  natural  genera,  or  those  genera  in  which 
the  species  are  most  closely  related  to  each  other,  are 
generally  confined  to  the  same  country,  or  if  they  have 
a  wide  range  that  their  range  is  continuous.  What  a 
strange  anomaly  it  would  be,  if  a  directly  opposite  rule 
were  to  prevail,  when  we  go  down  one  step  lower  in  the 
series,  namely,  to  the  individuals  of  the  same  species, 
and  these  had  not  been,  at  least  at  first,  confined  to  some 
one  region! 

Hence  it  seems  to  me,  as  it  has  to  many  other  natu- 
ralists, that  the  view  of  each  species  having  been  pro- 
duced in  one  area  alone,  and  having  subsequently  mi- 
grated from  that  area  as  far  as  its  powers  of  migration 
and  subsistence  under  past  and  present  conditions  per- 
mitted, is  the  most  probable.  Undoubtedly  many  cases 
occur,  in  which  we  cannot  explain  how  the  same  species 
could  have  passed  from  one  point  to  the  other.  But 
the  geographical  and  climatal  changes  which  have  cer- 
tainly occurred  within  recent  geological  times,  must 
have  rendered  discontinuous  the  formerly  continuous 
range  of  many  species.  So  that  we  are  reduced  to  con- 
sider whether  the  exceptions  to  continuity  of  range  are 
so  numerous  and  of  so  grave  a  nature,  that  we  ought  to 
give  up  the  belief,  rendered  probable  by  general  con- 
siderations, that  each  species  has  been  produced  within 
one  area,  and  has  migrated  thence  as  far  as  it  could. 
33 


13S  SINGLE  CENTRES  OP  CREATION.  [CHAP.  XIL 

It  would  be  hopelessly  tedious  to  discuss  all  the  excep- 
tional cases  of  the  same  species,  now  living  at  distant 
and  separated  points,  nor  do  I  for  a  moment  pretend  that 
any  explanation  could  be  offered  of  many  instances. 
But,  after  some  preliminary  remarks,  I  will  discuss  a 
few  of  the  most  striking  classes  of  facts;  namely,  the 
existence  of  the  same  species  on  the  summits  of  distant 
mountain  ranges,  and  at  distant  points  in  the  arctic  and 
antarctic  regions;  and  secondly  (in  the  following  chap- 
ter), the  wide  distribution  of  freshwater  productions; 
and  thirdly,  the  occurrence  of  the  same  terrestrial  species 
on  islands  and  on  the  nearest  mainland,  though  sepa- 
rated by  hundreds  of  miles  of  open  sea.  If  the  exist- 
ence of  the  same  species  at  distant  and  isolated  points 
of  the  earth's  surface,  can  in  many  instances  be  explained 
on  the  view  of  each  species  having  migrated  from  a 
single  birthplace;  then,  considering  our  ignorance  with 
respect  to  former  climatal  and  geographical  changes  and 
to  the  various  occasional  means  of  transport,  the  belief 
that  a  single  birthplace  is  the  law,  seems  to  me  incom- 
parably the  safest. 

In  discussing  this  subject,  we  shall  be  enabled  at  the 
same  time  to  consider  a  point  equally  important  for  us, 
namely,  whether  the  several  species  of  a  genus  which 
must  on  our  theory  all  be  descended  from  a  common 
progenitor,  can  have  migrated,  undergoing  modifica- 
tion during  their  migration,  from  some  one  area.  If, 
when  most  of  the  species  inhabiting  one  region  are  dif- 
ferent from  those  of  another  region,  though  closely 
allied  to  them,  it  can  be  shown  that  migration  from  the 
one  region  to  the  other  has  probably  occurred  at  some 
former  period,  our  general  view  will  be  much  strength- 
ened; for  the  explanation  is  obvious  on  the  principle  of 


CHAP.  XII.]  SINGLE  CENTRES  OP  CREATION.  139 

descent  with  modification.  A  volcanic  island,  for  in- 
stance, upheaved  and  formed  at  the  distance  of  a  few 
hundreds  of  miles  from  a  continent,  would  probably  re- 
ceive from  it  in  the  course  of  time  a  few  colonists,  and 
their  descendants,  though  modified,  would  still  be  re- 
lated by  inheritance  to  the  inhabitants  of  that  continent. 
Cases  of  this  nature  are  common,  and  are,  as  we  shall 
hereafter  see,  inexplicable  on  the  theory  of  independ- 
ent creation.  This  view  of  the  relation  of  the  species  of 
one  region  to  those  of  another,  does  not  differ  much 
from  that  advanced  by  Mr.  Wallace,  who  concludes  that 
"  every  species  has  come  into  existence  coincident  both 
in  space  and  time  with  a  pre-existing  closely  allied  spe- 
cies." And  it  is  now  well  known  that  he  attributes  this 
coincidence  to  descent  with  modification. 

The  question  of  single  or  multiple  centres  of  crea- 
tion differs  from  another  though  allied  question, — 
namely,  whether  all  the  individuals  of  the  same  species 
are  descended  from  a  single  pair,  or  single  hermaphrodite, 
or  whether,  as  some  authors  suppose,  from  many  individ- 
uals simultaneously  created.  With  organic  beings  which 
never  intercross,  if  such  exist,  each  species  must  be  de- 
scended from  a  succession  of  modified  varieties,  that 
have  supplanted  each  other,  but  have  never  blended 
with  other  individuals  or  varieties  of  the  same  species; 
BO  that,  at  each  successive  stage  of  modification,  all  the 
individuals  of  the  same  form  will  be  descended  from  a 
single  parent.  But  in  the  great  majority  of  cases,  name- 
ly, with  all  organisms  which  habitually  unite  for  each 
birth,  or  which  occasionally  intercross,  the  individuals 
of  the  same  species  inhabiting  the  same  area  will  be  kept 
nearly  uniform  by  intercrossing;  so  that  many  individ- 
uals will  go  on  simultaneously  changing,  and  the  whole 


140  MEANS  OP  DISPERSAL.  [CHAP.  XII. 

amount  of  modification  at  each  stage  will  not  be  due  to 
descent  from  a  single  parent.  To  illustrate  what  I 
mean:  our  English  race-horses  differ  from  the  horses  of 
every  other  breed;  but  they  do  not  owe  their  difference 
and  superiority  to  descent  from  any  single  pair,  but  to 
continued  care  in  the  selecting  and  training  of  many  in- 
dividuals during  each  generation. 

Before  discussing  the  three  classes  of  facts,  which  I 
have  selected  as  presenting  the  greatest  amount  of  diffi- 
culty on  the  theory  of  "  single  centres  of  creation,"  I 
must  say  a  few  words  on  the  means  of  dispersal. 

Means  of  Dispersal. 

Sir  C.  Lyell  and  other  authors  have  ably  treated 
this  subject.  I  can  give  here  only  the  briefest  abstract 
of  the  more  important  facts.  Change  of  climate  must 
have  had  a  powerful  influence  on  migration.  A  region 
now  impassable  to  certain  organisms  from  the  nature  of 
its  climate,  might  have  been  a  high  road  for  migration, 
when  the  climate  was  different.  I  shall,  however,  pres- 
ently have  to  discuss  this  branch  of  the  subject  in  some 
detail.  Changes  of  level  in  the  land  must  also  have 
been  highly  influential:  a  narrow  isthmus  now  sepa- 
rates two  marine  faunas;  submerge  it,  or  let  it  formerly 
have  been  submerged,  and  the  two  faunas  will  now 
blend  together,  or  may  formerly  have  blended.  Where 
the  sea  now  extends,  land  may  at  a  former  period  have 
connected  islands  or  possibly  even  continents  together, 
and  thus  have  allowed  terrestrial  productions  to  pass 
from  one  to  the  other.  No  geologist  disputes  that 
great  mutations  of  level  have  occurred  within  the  period 
of  existing  organisms.  Edward  Forbes  insisted  that  all 
the  islands  in  the  Atlantic  must  have  been  recently 


CHAP.  XII.]  MEANS  OF  DISPERSAL.  141 

connected  with  Europe  or  Africa,  and  Europe  likewise 
with  America.  Other  authors  have  thus  hypothetically 
bridged  over  every  ocean,  and  united  almost  every  is- 
land with  some  mainland.  If  indeed  the  arguments 
used  by  Forbes  are  to  be  trusted,  it  must  be  admitted 
that  scarcely  a  single  island  exists  which  has  not  re- 
cently been  united  to  some  continent.  This  view  cuts 
the  Gordian  knot  of  the  dispersal  of  the  same  species  to 
the  more  distant  points,  and  removes  many  a  difficulty; 
but  to  the  best  of  my  judgment  we  are  not  authorised  in 
admitting  such  enormous  geographical  changes  within 
the  period  of  existing  species.  It  seems  to  me  that  we 
have  abundant  evidence  of  great  oscillations  in  the  level 
of  the  land  or  sea;  but  not  of  such  vast  change  in  the 
position  and  extension  of  our  continents,  as  to  have 
united  them  within  the  recent  period  to  each  other  and 
to  the  several  intervening  oceanic  islands.  I  freely  ad- 
mit the  former  existence  of  many  islands,  now  buried 
beneath  the  sea,  which  may  have  served  as  halting-places 
for  plants  and  for  many  animals  during  their  migration. 
In  the  coral-producing  oceans  such  sunken  islands  are 
now  marked  by  rings  of  coral  or  atolls  standing  over 
them.  Whenever  it  is  fully  admitted,  as  it  will  some 
day  be,  that  each  species  has  proceeded  from  a  single 
birthplace,  and  when  in  the  course  of  time  we  know 
something  definite  about  the  means  of  distribution,  we 
shall  be  enabled  to  speculate  with  security  on  the  for- 
mer extension  of  the  land.  But  I  do  not  believe  that  it 
will  ever  be  proved  that  within  the  recent  period  most 
of  our  continents  which  now  stand  quite  separate  have 
been  continuously,  or  almost  continuously  united  with 
each  other,  and  with  the  many  existing  oceanic  islands. 
Several  facts  in  distribution, — such  as  thegreat  difference 


142  MEANS  OF  DISPERSAL.  [CHAP.  XIL 

in  the  marine  faunas  on  the  opposite  sides  of  almost 
every  continent, — the  close  relation  of  the  tertiary  in- 
habitants of  several  lands  and  even  seas  to  their  present 
inhabitants, — the  degree  of  affinity  between  the  mam- 
mals inhabiting  islands  with  those  of  the  nearest  conti- 
nent, being  in  part  determined  (as  we  shall  hereafter 
see)  by  the  depth  of  the  intervening  ocean, — these  and 
other  such  facts  are  opposed  to  the  admission  of  such 
prodigious  geographical  revolutions  within  the  recent 
period,  as  are  necessary  on  the  view  advanced  by  Forbes 
and  admitted  by  his  followers.  The  nature  and  rela- 
tive proportions  of  the  inhabitants  of  oceanic  islands  are 
likewise  opposed  to  the  belief  of  their  former  continu- 
ity with  continents.  Nor  does  the  almost  universally 
volcanic  composition  of  such  islands  favour  the  admis- 
sion that  they  are  the  wrecks  of  sunken  continents; — if 
they  had  originally  existed  as  continental  mountain 
ranges,  some  at  least  of  the  islands  would  have  been 
formed,  like  other  mountain  summits,  of  granite,  meta- 
morphic  schists,  old  fossiliferous  and  other  rocks,  instead 
of  consisting  of  mere  piles  of  volcanic  matter. 

I  must  now  say  a  few  words  on  what  are  called 
accidental  means,  but  which  more  properly  should  be 
called  occasional  means  of  distribution.  I  shall  here 
confine  myself  to  plants.  In  botanical  works,  this  or 
that  plant  is  often  stated  to  be  ill  adapted  for  wide  dis- 
semination; but  the  greater  or  less  facilities  for  trans- 
port across  the  sea  may  be  said  to  be  almost  wholly 
unknown.  Until  I  tried,  with  Mr.  Berkeley's  aid,  a  few 
experiments,  it  was  not  even  known  how  far  seeds  could 
resist  the  injurious  action  of  sea-water.  To  my  sur- 
prise I  found  that  out  of  87  kinds,  64  germinated  after 
an  immersion  of  28  days,  and  a  few  survived  an  immer- 


CHAP.  XII.]  MEANS  OP  DISPERSAL.  143 

sion  of  137  days.  It  deserves  notice  that  certain  orders 
were  far  more  injured  than  others:  nine  LeguminosaB 
were  tried,  and,  with  one  exception,  they  resisted  the 
salt-water  badly;  seven  species  of  the  allied  orders,  Hy- 
drophyllaceae  and  Polemoniaceac,  were  all  killed  by  a 
month's  immersion.  For  convenience'  sake  I  chiefly 
tried  small  seeds  without  the  capsule  or  fruit;  and  as 
all  of  these  sank  in  a  few  days  they  could  not  have  been 
floated  across  wide  spaces  of  the  sea,  whether  or  not  they 
were  injured  by  the  salt-water.  Afterwards  I  tried  some 
larger  fruits,  capsules,  &c.,  and  some  of  these  floated  for 
a  long  time.  It  is  well  known  what  a  difference  there 
is  in  the  buoyancy  of  green  and  seasoned  timber;  and  it 
occurred  to  me  that  floods  would  often  wash  into  the 
sea  dried  plants  or  branches  with  seed-capsules  or  fruit 
attached  to  them.  Hence  I  was  led  to  dry  the  stems 
and  branches  of  94  plants  with  ripe  fruit,  and  to  place 
them  on  sea-water.  The  majority  sank  rapidly,  but 
some  which,  whilst  green,  floated  for  a  short  time,  when 
dried  floated  much  longer;  for  instance,  ripe  hazel- 
nuts  sank  immediately,  but  when  dried  they  floated  for 
90  days,  and  afterwards  when  planted  germinated;  an 
asparagus-plant  with  ripe  berries  floated  for  23  days, 
when  dried  it  floated  for  85  days,  and  the  seeds  after- 
wards germinated;  the  ripe  seeds  of  Helosciadium  sank 
in  two  days,  when  dried  they  floated  for  above  90  days, 
and  afterwards  germinated.  Altogether,  out  of  the  94 
dried  plants,  18  floated  for  above  28  days;  and  some  of 
the  18  floated  for  a  very  much  longer  period.  So  that 
as  ff-  kinds  of  seeds  germinated  after  an  immersion  of 
28  days;  and  as  ^  distinct  species  with  ripe  fruit  (but 
not  all  the  same  species  as  in  the  foregoing  experiment) 
floated,  after  being  dried,  for  above  28  days,  we  may 


144  MEANS  OF  DISPERSAL.  [CHAP.  XII. 

conclude,  as  far  as  anything  can  be  inferred  from  these 
scanty  facts,  that  the  seeds  of  -j^fo  kinds  of  plants  of  any 
country  might  be  floated  by  sea-currents  during  28  days, 
and.  would  retain  their  power  of  germination.  In 
Johnston's  Physical  Atlas,  the  average  rate  of  the  sev- 
eral Atlantic  currents  is  33  miles  per  diem  (some  cur- 
rents running  at  the  rate  of  60  miles  per  diem);  on  this 
average,  the  seeds  of  y1^  plants  belonging  to  one  coun- 
try might  be  floated  across  924  miles  of  sea  to  another 
country,  and  when  stranded,  if  blown  by  an  inland  gale 
to  a  favourable  spot,  would  germinate. 

Subsequently  to  my  experiments,  M.  Martens  tried 
similar  ones,  but  in  a  much  better  manner,  for  he  placed 
the  seeds  in  a  box  in  the  actual  sea,  so  that  they  were 
alternately  wet  and  exposed  to  the  air  like  really  float- 
ing plants.  He  tried  98  seeds,  mostly  different  from 
mine;  but  he  chose  many  large  fruits  and  likewise  seeds 
from  plants  which  live  near  the  sea;  and  this  would 
have  favoured  both  the  average  length  of  their  flota- 
tion and  their  resistance  to  the  injurious  action  of  the 
salt-water.  On  the  other  hand,  he  did  not  previously 
dry  the  plants  or  branches  with  the  fruit;  and  this,  as 
we  have  seen,  would  have  caused  some  of  them  to  have 
floated  much  longer.  The  result  was  that  ^f  of  his 
seeds  of  different  kinds  floated  for  42  days,  and  were 
then  capable  of  germination.  But  I  do  not  doubt  that 
plants  exposed  to  the  waves  would  float  for  a  less  time 
than  those  protected  from  violent  movement  as  in  our 
experiments.  Therefore  it  would  perhaps  be  safer  to 
assume  that  the  seeds  of  about  j^  plants  of  a  flora, 
after  having  been  dried,  could  be  floated  across  a  space 
of  sea  900  miles  in  width,  and  would  then  germinate. 
The  fact  of  the  larger  fruits  often  floating  longer  than 


CHAP.  XII.]  MEANS  OP  DISPERSAL.  145 

the  small,  is  interesting;  as  plants  with  large  seeds  or 
fruit  which,  as  Alph.  de  Candolle  has  shown,  generally 
have  restricted  ranges,  could  hardly  be  transported  by 
any  other  means. 

Seeds  may  be  occasionally  transported  in  another 
manner.  Drift  timber  is  thrown  up  on  most  islands, 
even  on  those  in  the  midst  of  the  widest  oceans;  and 
the  natives  of  the  coral-islands  in  the  Pacific  procure 
stones  for  their  tools,  solely  from  the  roots  of  drifted 
trees,  these  stones  being  a  valuable  royal  tax.  I  find 
that  when  irregularly  shaped  stones  are  embedded  in 
the  roots  of  trees,  small  parcels  of  earth  are  frequently 
enclosed  in  their  interstices  and  behind  them, — so  per- 
fectly that  not  a  particle  could  be  washed  away  during 
the  longest  transport:  out  of  one  small  portion  of  earth 
thus  completely  enclosed  by  the  roots  of  an  oak  about  50 
years  old,  three  dicotyledonous  plants  germinated:  I  am 
certain  of  the  accuracy  of  this  observation.  Again,  I 
can  show  that  the  carcases  of  birds,  when  floating  on  the 
sea,  sometimes  escape  being  immediately  devoured:  and 
many  kinds  of  seeds  in  the  crops  of  floating  birds  long 
retain  their  vitality:  peas  and  vetches,  for  instance,  are 
killed  by  even  a  few  days'  immersion  in  sea- water;  but 
some  taken  out  of  the  crop  of  a  pigeon,  which  had  floated 
on  artificial  sea-water  for  30  days,  to  my  surprise  nearly 
all  germinated. 

Living  birds  can  hardly  fail  to  be  highly  effective 
agents  in  the  transportation  of  seeds.  I  could  give 
many  facts  showing  how  frequently  birds  of  many  kinds 
are  blown  by  gales  to  vast  distances  across  the  ocean. 
We  may  safely  assume  that  under  such  circumstances 
their  rate  of  flight  would  often  be  35  miles  an  hour; 
and  some  authors  have  given  a  far  higher  estimate.  I 


146  MEANS  OF  DISPERSAL.  [CHAfr.  XII. 

have  never  seen  an  instance  of  nutritious  seeds  passing 
through  the  intestines  of  a  bird;  but  hard  seeds  of  fruit 
pass  uninjured  through  even  the  digestive  organs  of  a 
turkey.  In  the  course  of  two  months,  I  picked  up  in 
my  garden  12  kinds  of  seeds,  out  of  the  excrement  of 
small  birds,  and  these  seemed  perfect,  and  some  of 
them,  which  were  tried,  germinated.  But  the  following 
fact  is  more  important:  the  crops  of  birds  do  not  secrete 
gastric  juice,  and  do  not,  as  I  know  by  trial,  injure  in 
the  least  the  germination  of  seeds;  now,  after  a  bird 
has  found  and  devoured  a  large  supply  of  food,  it  is 
positively  asserted  that  all  the  grains  do  not  pass  into 
the  gizzard  for  twelve  or  even  eighteen  hours.  A  bird  in 
this  interval  might  easily  be  blown  to  the  distance  of 
500  miles,  and  hawks  are  known  to  look  out  for  tired 
birds,  and  the  contents  of  their  torn  crops  might  thus 
readily  get  scattered.  Some  hawks  and  owls  bolt  their 
prey  whole,  and,  after  an  interval  of  from  twelve  to 
twenty  hours,  disgorge  pellets,  which,  as  I  know  from 
experiments  made  in  the  Zoological  Gardens,  include 
seeds  capable  of  germination.  Some  seeds  of  the  oat, 
wheat,  millet,  canary,  hemp,  clover,  and  beet  germi- 
nated after  having  been  from  twelve  to  twenty-one  hours 
in  the  stomachs  of  different  birds  of  prey;  and  two 
seeds  of  beet  grew  after  having  been  thus  retained  for 
two  days  and  fourteen  hours.  Fresh-water  fish,  I  find, 
eat  seeds  of  many  land  and  water  plants;  fish  are  fre- 
quently devoured  by  birds,  and  thus  the  seeds  might 
be  transported  from  place  to  place.  I  forced  many 
kinds  of  seeds  into  the  stomachs  of  dead  fish,  and  then 
gave  their  bodies  to  fishing-eagles,  storks,  and  pelicans; 
these  birds,  after  an  interval  of  many  hours,  either  re- 
jected the  seeds  in  pellets  or  passed  them  in  their  excre- 


CHAP.  XII.]  MEANS  OP  DISPERSAL.  147 

rnent;  arid  several  of  these  seeds  retained  the  power  of 
germination.  Certain  seeds,  however,  were  always 
killed  by  this  process. 

Locusts  are  sometimes  blown  to  great  distances  from 
the  land;  I  myself  caught  one  370  miles  from  the  coast 
of  Africa,  and  have  heard  of  others  caught  at  greater 
distances.  The  Rev.  R.  T.  Lowe  informed  Sir  C.  Lyell 
that  in  November  1844  swarms  of  locusts  visited  the 
island  of  Madeira.  They  were  in  countless  numbers,  as 
thick  as  the  flakes  of  snow  in  the  heaviest  snowstorm, 
and  extended  upwards  as  far  as  could  be  seen  with  a 
telescope.  During  two  or  three  days  they  slowly  ca- 
reered round  and  round  in  an  immense  ellipse,  at  least 
five  or  six  miles  in  diameter,  and  at  night  alighted  on 
the  taller  trees,  which  were  completely  coated  with 
them.  They  then  disappeared  over  the  sea,  as  suddenly 
as  they  had  appeared,  and  have  not  since  visited  the 
island.  Now,  in  parts  of  Natal  it  is  believed  by  some 
farmers,  though  on  insufficient  evidence,  that  injurious 
seeds  are  introduced  into  their  grass-land  in  the  dung 
left  by  the  great  flights  of  locusts  which  often  visit  that 
country.  In  consequence  of  this  belief  Mr.  Weale  sent 
me  in  a  letter  a  small  packet  of  the  dried  pellets,  out  of 
which  I  extracted  under  the  microscope  several  seeds, 
and  raised  from  them  seven  grass  plants,  belonging  to 
two  species,  of  two  genera.  Hence  a  swarm  of  locusts, 
such  as  that  which  visited  Madeira,  might  readily  be  the 
means  of  introducing  several  kinds  of  plants  into  an 
island  lying  far  from  the  mainland. 

Although  the  beaks  and  feet  of  birds  are  generally 
clean,  earth  sometimes  adheres  to  them:  in  one  case  I 
removed  sixty-one  grains,  and  in  another  case  twenty- 
two  grains  of  dry  argillaceous  earth  from  the  foot  of  a 


148  MEANS  OF  DISPERSAL.  [CHAP.  XII. 

partridge,  and  in  the  earth  there  was  a  pebble  as  large  as 
the  seed  of  a  vetch.  Here  is  a  better  case:  the  leg  of  a 
woodcock  was  sent  to  me  by  a  friend,  with  a  little  cake 
of  dry  earth  attached  to  the  shank,  weighing  only  nine 
grains;  and  this  contained  a  seed  of  the  toad-rush  (Jun- 
cus  bufonius)  which  germinated  and  flowered.  Mr. 
Swaysland,  of  Brighton,  who  during  the  last  forty  years 
has  paid  close  attention  to  our  migratory  birds,  informs 
me  that  he  has  often  shot  wagtails  (Motacillag),  wheat- 
ears,  and  whinchats  (Saxicolas),  on  their  first  arrival  on 
our  shores,  before  they  had  alighted;  and  he  has  several 
times  noticed  little  cakes  of  earth  attached  to  their  feet. 
Many  facts  could  be  given  showing  how  generally  soil 
is  charged  with  seeds.  For  instance,  Prof.  Newton  sent 
me  the  leg  of  a  red-legged  partridge  (Caccabis  rufa) 
which  had  been  wounded  and  could  not  fly,  with  a  ball 
of  hard  earth  adhering  to  it,  and  weighing  six  and  a  half 
ounces.  The  earth  had  been  kept  for  three  years,  but 
when  broken,  watered  and  placed  under  a  bell  glass,  no 
less  than  82  plants  sprung  from  it:  these  consisted  of 
12  monocotyledons,  including  the  common  oat,  and  at 
least  one  kind  of  grass,  and  of  70  dicotyledons,  which 
consisted,  judging  from  the  young  leaves,  of  at  least 
three  distinct  species.  With  such  facts  before  us,  can 
we  doubt  that  the  many  birds  which  are  annually 
blown  by  gales  across  great  spaces  of  ocean,  and 
which  annually  migrate — for  instance,  the  millions  of 
quails  across  the  Mediterranean — must  occasionally 
transport  a  few  seeds  embedded  in  dirt  adhering  to 
their  feet  or  beaks?  But  I  shall  have  to  recur  to  this 
subject. 

As  icebergs  are  known  to  be  sometimes  loaded  with 
earth  and  stones,  and  have  even  carried  brushwood, 


CHAP.  XII.]  MEANS  OP  DISPERSAL.  149 

bones,  and  the  nest  of  a  land-bird,  it  can  hardly  be 
doubted  that  they  must  occasionally,  as  suggested  by 
Lyell,  have  transported  seeds  from  one  part  to  another 
of  the  arctic  and  antarctic  regions;  and  during  the 
Glacial  period  from  one  part  of  the  now  temperate 
regions  to  another.  In  the  Azores,  from  the  large 
number  of  plants  common  to  Europe,  in  comparison 
with  the  species  on  the  other  islands  of  the  Atlantic, 
which  stand  nearer  to  the  mainland,  and  (as  remarked 
by  Mr.  H.  C.  Watson)  from  their  somewhat  northern 
character  in  comparison  with  the  latitude,  I  suspected 
that  these  islands  had  been  partly  stocked  by  ice-borne 
seeds,  during  the  Glacial  epoch.  At  my  request  Sir  C. 
Lyell  wrote  to  M.  Hartung  to  inquire  whether  he  had 
observed  erratic  boulders  on  these  islands,  and  he 
answered  that  he  had  found  large  fragments  of  granite 
and  other  rocks,  which  do  not  occur  in  the  archipelago. 
Hence  we  may  safely  infer  that  icebergs  formerly 
landed  their  rocky  burthens  on  the  shores  of  these 
mid-ocean  islands,  and  it  is  at  least  possible  that  they 
may  have  brought  thither  some  few  seeds  of  northern 
plants. 

Considering  that  these  several  means  of  transport, 
and  that  other  means,  which  without  doubt  remain  to 
be  discovered,  have  been  in  action  year  after  year  for 
tens  of  thousands  of  years,  it  would,  I  think,  be  a  mar- 
vellous fact  if  many  plants  had  not  thus  become  widely 
transported.  These  means  of  transport  are  sometimes 
called  accidental,  but  this  is  not  strictly  correct:  the 
currents  of  the  sea  are  not  accidental,  nor  is  the  direc- 
tion of  prevalent  gales  of  wind.  It  should  be  observed 
that  scarcely  any  means  of  transport  would  carry  seeds 
for  very  great  distances:  for  seeds  do  not  retain  their 


150  MEANS  OP  DISPERSAL.  [CHAP.  XII. 

vitality  when  exposed  for  a  great  length  of  time  to  the 
action  of  sea-water;  nor  could  they  be  long  carried  in 
the  crops  or  intestines  of  birds.  These  means,  how- 
ever, would  suffice  for  occasional  transport  across  tracts 
of  sea  some  hundred  miles  in  breadth,  or  from  island 
to  island,  or  from  a  continent  to  a  neighbouring  island, 
but  not  from  one  distant  continent  to  another.  The 
floras  of  distant  continents  would  not  by  such  means 
become  mingled;  but  would  remain  as  distinct  as  they 
now  are.  The  currents,  from  their  course,  would  never 
bring  seeds  from  North  America  to  Britain,  though 
they  might  and  do  bring  seeds  from  the  West  Indies 
to  our  western  shores,  where,  if  not  killed  by  their  very 
long  immersion  in  salt  water,  they  could  not  endure  our 
climate.  Almost  every  year,  one  or  two  land-birds  are 
blown  across  the  whole  Atlantic  Ocean,  from  North 
America  to  the  western  shores  of  Ireland  and  England; 
but  seeds  could  be  transported  by  these  rare  wanderers 
only  by  one  means,  namely,  by  dirt  adhering  to  their 
feet  or  beaks,  which  is  in  itself  a  rare  accident.  Even  in 
this  case,  how  small  would  be  the  chance  of  a  seed  fall- 
ing on  favourable  soil,  and  coming  to  maturity!  But  it 
would  be  a  great  error  to  argue  that  because  a  well- 
stocked  island,  like  Great  Britain,  has  not,  as  far  as 
is  known  (and  it  would  be  very  difficult  to  prove  this), 
received  within  the  last  few  centuries,  through  occa- 
sional means  of  transport,  immigrants  from  Europe  or 
any  other  continent,  that  a  poorly-stocked  island, 
though  standing  more  remote  from  the  mainland,  would 
not  receive  colonists  by  similar  means.  Out  of  a  hun- 
dred kinds  of  seeds  or  animals  transported  to  an  island, 
even  if  far  less  well-stocked  than  Britain,  perhaps  not 
more  than  one  would  be  so  well  fitted  to  its  new  home, 


CHAP.  XII.]  THE  GLACIAL  PEKIOD.  151 

as  to  become  naturalised.  But  this  is  no  valid  argu- 
ment against  what  would  be  effected  by  occasional 
means  of  transport,  during  the  long  lapse  of  geologi- 
cal time,  whilst  the  island  was  being  upheaved,  and 
before  it  had  become  fully  stocked  with  inhabitants. 
On  almost  bare  land,  with  few  or  no  destructive  in- 
sects or  birds  living  there,  nearly  every  seed  which 
chanced  to  arrive,  if  fitted  for  the  climate,  would  ger- 
minate and  survive. 

Dispersal  during  the  Glacial  Period. 

The  identity  of  many  plants  and  animals,  on  moun- 
tain-summits, separated  from  each  other  by  hundreds 
of  miles  of  lowlands,  where  Alpine  species  could  not 
possibly  exist,  is  one  of  the  most  striking  cases  known 
of  the  same  species  living  at  distant  points,  without  the 
apparent  possibility  of  their  having  migrated  from  one 
point  to  the  other.  It  is  indeed  a  remarkable  fact  to 
see  so  many  plants  of  the  same  species  living  on  the 
snowy  regions  of  the  Alps  or  Pyrenees,  and  in  the  ex- 
treme northern  parts  of  Europe;  but  it  is  far  more  re- 
markable, that  the  plants  on  the  White  Mountains,  in 
the  United  States  of  America,  are  all  the  same  with 
those  of  Labrador,  and  nearly  all  the  same,  as  we  hear 
from  Asa  Gray,  with  those  on  the  loftiest  mountains 
of  Europe.  Even  as  long  ago  as  1747,  such  facts  led 
Gmelin  to  conclude  that  the  same  species  must  have 
been  independently  created  at  many  distinct  points; 
and  we  might  have  remained  in  this  same  belief,  had 
not  Agassiz  and  others  called  vivid  attention  to  the 
Glacial  period,  which,  as  we  shall  immediately  see, 
affords  a  simple  explanation  of  these  facts.  "We  have 
evidence  of  almost  every  conceivable  kind,  organic  and 


152  DISPERSAL  DURING  [CHAP.  XII. 

inorganic,  that,  within  a  very  recent  geological  period, 
central  Europe  and  North  America  suffered  under  an 
arctic  climate.  The  ruins  of  a  house  burnt  by  fire  do 
not  tell  their  tale  more  plainly  than  do  the  mountains 
of  Scotland  and  Wales,  with  their  scored  flanks,  pol- 
ished surfaces,  and  perched  boulders,  of  the  icy  streams 
with  which  their  valleys  were  lately  filled.  So  greatly 
has  the  climate  of  Europe  changed,  that  in  Northern 
Italy,  gigantic  moraines,  left  by  old  glaciers,  are  now 
clothed  by  the  vine  and  maize.  Throughout  a  large 
part  of  the  United  States,  erratic  boulders  and  scored 
rocks  plainly  reveal  a  former  cold  period. 

The  former  influence  of  the  glacial  climate  on  the 
distribution  of  the  inhabitants  of  Europe,  as  explained 
by  Edward  Forbes,  is  substantially  as  follows.  But  we 
shall  follow  the  changes  more  readily,  by  supposing  a 
new  glacial  period  slowly  to  come  on,  and  then  pass 
away,  as  formerly  occurred.  As  the  cold  came  on,  and 
as  each  more  southern  zone  became  fitted  for  the  in- 
habitants of  the  north,  these  would  take  the  places  of 
the  former  inhabitants  of  the  temperate  regions.  The 
latter,  at  the  same  time,  would  travel  further  and  fur- 
ther southward,  unless  they  were  stopped  by  barriers, 
in  which  case  they  would  perish.  The  mountains 
would  become  covered  with  snow  and  ice,  and  their  for- 
mer Alpine  inhabitants  would  descend  to  the  plains. 
By  the  time  that  the  cold  had  reached  its  maximum,  we 
should  have  an  arctic  fauna  and  flora,  covering  the 
central  parts  of  Europe,  as  far  south  as  the  Alps  and 
Pyrenees,  and  even  stretching  into  Spain.  The  now 
temperate  regions  of  the  United  States  would  likewise 
be  covered  by  arctic  plants  and  animals  and  these  would 
"be  nearly  the  same  with  those  of  Europe;  for  the 


CHAP.  XII.]  THE  GLACIAL  PERIOD.  153 

present  circumpolar  inhabitants,  which  we  suppose  to 
have  everywhere  travelled  southward,  are  remarkably 
uniform  round  the  world. 

As  the  warmth  returned,  the  arctic  forms  would 
retreat  northward,  closely  followed  up  in  their  retreat 
by  the  productions  of  the  more  temperate  regions.  And 
as  the  snow  melted  from  the  bases  of  the  mountains, 
the  arctic  forms  would  seize  on  the  cleared  and  thawed 
ground,  always  ascending,  as  the  warmth  increased  and 
the  snow  still  further  disappeared,  higher  and  higher, 
whilst  their  brethren  were  pursuing  their  northern 
journey.  Hence,  when  the  warmth  had  fully  returned, 
the  same  species,  which  had  lately  lived  together  on  the 
European  and  North  American  lowlands,  would  again 
be  found  in  the  arctic  regions  of  the  Old  and  New 
Worlds,  and  on  many  isolated  mountain-summits  far 
distant  from  each  other. 

Thus  we  can  understand  the  identity  of  many  plants 
at  points  so  immensely  remote  as  the  mountains  of  the 
United  States  and  those  of  Europe.  We  can  thus  also 
understand  the  fact  that  the  Alpine  plants  of  each 
mountain-range  are  more  especially  related  to  the  arctic 
forms  living  due  north  or  nearly  due  north  of  them: 
for  the  first  migration  when  the  cold  came  on,  and  the 
re-migration  on  the  returning  warmth,  would  generally 
have  been  due  south  and  north.  The  Alpine  plants, 
for  example,  of  Scotland,  as  remarked  by  Mr.  H.  C. 
Watson,  and  those  of  the  Pyrenees,  as  remarked  by 
Ramond,  are  more  especially  allied  to  the  plants  of 
northern  Scandinavia;  those  of  the  United  States  to 
Labrador;  those  of  the  mountains  of  Siberia  to  the 
arctic  regions  of  that  country.  These  views,  grounded 

as  they  are  on  the  perfectly  well-ascertained  occurrence 
36 


154:  DISPERSAL  DURING  [CiiAP.  XII. 

of  a  former  Glacial  period,  seem  to  me  to  explain  in  so 
satisfactory  a  manner  the  present  distribution  of  the 
Alpine  and  Arctic  productions  of  Europe  and  America, 
that  when  in  other  regions  we  find  the  same  species 
on  distant  mountain-summits,  we  may  almost  conclude, 
without  other  evidence,  that  a  colder  climate  formerly 
permitted  their  migration  across  the  intervening  low- 
lands, now  become  too  warm  for  their  existence. 

As  the  arctic  forms  moved  first  southward  and  after- 
wards backwards  to  the  north,  in  unison  with  the  chang- 
ing climate,  they  will  not  have  been  exposed  during 
their  long  migrations  to  any  great  diversity  of  tem- 
perature; and  as  they  all  migrated  in  a  body  together, 
their  mutual  relations  will  not  have  been  much  dis- 
turbed. Hence,  in  accordance  with  the  principles  in- 
culcated in  this  volume,  these  forms  will  not  have  been 
liable  to  much  modification.  But  with  the  Alpine  pro- 
ductions, left  isolated  from  the  moment  of  the  return- 
ing warmth,  first  at  the  bases  and  ultimately  on  the 
summits  of  the  mountains,  the  case  will  have  been 
somewhat  different;  for  it  is  not  likely  that  all  the  same 
arctic  species  will  have  been  left  on  mountain-ranges 
far  distant  from  each  other,  and  have  survived  there 
ever  since;  they  will  also  in  all  probability,  have  become 
mingled  with  ancient  Alpine  species,  which  must  have 
existed  on  the  mountains  before  the  commencement  of 
the  Glacial  epoch,  and  which  during  the  coldest  period 
will  have  been  temporarily  driven  down  to  the  plains; 
they  will,  also,  have  been  subsequently  exposed  to  some- 
what different  climatal  influences.  Their  mutual  rela- 
tions will  thus  have  been  in  some  degree  disturbed;  con- 
sequently they  will  have  been  liable  to  modification;  and 
they  have  been  modified;  for  if  we  compare  the  present 


CHAP.  XII.]  THE  GLACIAL  PERIOD.  155 

Alpine  plants  and  animals  of  the  several  great  Euro- 
pean mountain-ranges  one  with  another,  though  many 
of  the  species  remain  identically  the  same,  some  exist 
as  varieties,  some  as  doubtful  forms  or  sub-species,  and 
some  as  distinct  yet  closely  allied  species  representing 
each  other  on  the  several  ranges. 

In  the  foregoing  illustration  I  have  assumed  that  at 
the  commencement  of  our  imaginary  Glacial  period, 
the  arctic  productions  were  as  uniform  round  the  polar 
regions  as  they  are  at  the  present  day.  But  it  is  also 
necessary  to  assume  that  many  sub-arctic  and  some  few 
temperate  forms  were  the  same  round  the  world,  for 
some  of  the  species  which  now  exist  on  the  lower  moun- 
tain-slopes and  on  the  plains  of  North  America  and 
Europe  are  the  same;  and  it  may  be  asked  how  I  ac- 
count for  this  degree  of  uniformity  in  the  sub-arctic 
and  temperate  forms  round  the  world,  at  the  commence- 
ment of  the  real  Glacial  period.  At  the  present  day,  the 
sub-arctic  and  northern  temperate  productions  of  the 
Old  and  New  Worlds  are  separated  from  each  other  by 
the  whole  Atlantic  Ocean  and  by  the  northern  part  of 
the  Pacific.  During  the  Glacial  period,  when  the  in- 
habitants of  the  Old  and  New  Worlds  lived  farther 
southwards  than  they  do  at  present,  they  must  have  been 
still  more  completely  separated  from  each  other  by 
wider  spaces  of  ocean;  so  that  it  may  well  be  asked  how 
the  same  species  could  then  or  previously  have  entered 
the  two  continents.  The  explanation,  I  believe,  lies  in 
the  nature  of  the  climate  before  the  commencement  of 
the  Glacial  period.  At  this,  the  newer  Pliocene  period, 
the  majority  of  the  inhabitants  of  the  world  were  specifi- 
cally the  same  as  now,  and  we  have  good  reason  to  be- 
lieve that  the  climate  was  warmer  than  at  the  present 


156  DISPERSAL  DURING  [CHAP.  XIL 

day.  Hence  we  may  suppose  that  the  organisms  which 
now  live  under  latitude  60°,  lived  during  the  Pliocene 
period  farther  north  under  the  Polar  Circle,  in  latitude 
66°-67°;  and  that  the  present  arctic  productions  then 
lived  on  the  broken  land  still  nearer  to  the  pole.  Now, 
if  we  look  at  a  terrestrial  globe,  we  see  under  the  Polar 
Circle  that  there  is  almost  continuous  land  from  wes- 
tern Europe,  through  Siberia,  to  eastern  America.  And 
this  continuity  of  the  circumpolar  land,  with  the  con- 
sequent freedom  under  a  more  favourable  climate  for  in- 
termigration,will  account  for  the  supposed  uniformity  of 
the  sub-arctic  and  temperate  productions  of  the  Old  and 
New  Worlds,  at  a  period  anterior  to  the  Glacial  epoch. 

Believing,  from  reasons  before  alluded  to,  that  our 
continents  have  long  remained  in  nearly  the  same  relative 
position,  though  subjected  to  great  oscillations  of  level, 
I  am  strongly  inclined  to  extend  the  above  view,  and 
to  infer  that  during  some  still  earlier  and  still  warmer 
period,  such  as  the  older  Pliocene  period,  a  large  num- 
ber of  the  same  plants  and  animals  inhabited  the  al- 
most continuous  circumpolar  land;  and  that  these  plants 
and  animals,  both  in  the  Old  and  New  Worlds,  began 
slowly  to  migrate  southwards  as  the  climate  became 
less  warm,  long  before  the  commencement  of  the  Glacial 
period.  We  now  see,  as  I  believe,  their  descendants, 
mostly  in  a  modified  condition,  in  the  central  parts  of 
Europe  and  the  United  States.  On  this  view  we  can 
understand  the  relationship  with  very  little  identity, 
between  the  productions  of  North  America  and  Europe, 
— a  relationship  which  is  highly  remarkable,  consider- 
ing the  distance  of  the  two  areas,  and  their  separation 
by  the  whole  Atlantic  Ocean.  We  can  further  under- 
stand the  singular  fact  remarked  on  by  several  observers 


CHAP.  XII.]  THE  GLACIAL  PERIOD.  157 

that  the  productions  of  Europe  and  America  during 
the  later  tertiary  stages  were  more  closely  related  to 
each  other  than  they  are  at  the  present  time;  for  dur- 
ing these  warmer  periods  the  northern  parts  of  the  Old 
and  New  Worlds  will  have  been  almost  continuously 
united  by  land,  serving  as  a  bridge,  since  rendered 
impassable  by  cold,  for  the  intermigration  of  their  in- 
habitants. 

During  the  slowly  decreasing  warmth  of  the  Plio- 
cene period,  as  soon  as  the  species  in  common,  which  in- 
habited the  New  and  Old  "Worlds,  migrated  south  of 
the  Polar  Circle,  they  will  have  been  completely  cut  off 
from  each  other.  This  separation,  as  far  as  the  more 
temperate  productions  are  concerned,  must  have  taken 
place  long  ages  ago.  As  the  plants  and  animals  mi- 
grated southward,  they  will  have  become  mingled  in  the 
one  great  region  with  the  native  American  productions, 
and  would  have  had  to  compete  with  them;  and  in  the 
other  great  region,  with  those  of  the  Old  World.  Con- 
sequently we  have  here  everything  favourable  for  much 
modification, — for  far  more  modification  than  with  the 
Alpine  productions,  left  isolated,  within  a  much  more 
recent  period,  on  the  several  mountain-ranges  and  on 
the  arctic  lands  of  Europe  and  N.  America.  Hence  it 
has  come,  that  when  we  compare  the  now  living  pro- 
ductions of  the  temperate  regions  of  the  New  and  Old 
Worlds,  we  find  very  few  identical  species  (though  Asa 
Gray  has  lately  shown  that  more  plants  are  identical 
than  was  formerly  supposed),  but  we  find  in  every  great 
class  many  forms,  which  some  naturalists  rank  as  geo- 
graphical races,  and  others  as  distinct  species;  and  a 
host  of  closely  allied  or  representative  forms  which  are 
ranked  by  all  naturalists  as  specifically  distinct. 


158  ALTERNATE  GLACIAL  PERIODS    [CHAP.  XII. 

As  on  the  land,  so  in  the  waters  of  the  sea,  a  slow 
southern  migration  of  a  marine  fauna,  which,  during 
the  Pliocene  or  even  a  somewhat  earlier  period,  was 
nearly  uniform  along  the  continuous  shores  of  the  Polar 
Circle,  will  account,  on  the  theory  of  modification,  for 
many  closely  allied  forms  now  living  in  marine  areas 
completely  sundered.  Thus,  I  think,  we  can  under- 
stand the  presence  of  some  closely  allied,  still  existing 
and  extinct  tertiary  forms,  on  the  eastern  and  western 
shores  of  temperate  North  America;  and  the  still  more 
striking  fact  of  many  closely  allied  crustaceans  (as  de- 
scribed in  Dana's  admirable  work),  some  fish  and  other 
marine  animals,  inhabiting  the  Mediterranean  and  the 
seas  of  Japan, — these  two  areas  being  now  completely 
separated  by  the  breadth  of  a  whole  continent  and  by 
wide  spaces  of  ocean. 

These  cases  of  close  relationship  in  species  either 
now  or  formerly  inhabiting  the  seas  on  the  eastern  and 
western  shores  of  North  America,  the  Mediterranean 
and  Japan,  and  the  temperate  lands  of  North  America 
and  Europe,  are  inexplicable  on  the  theory  of  creation. 
We  cannot  maintain  that  such  species  have  been  created 
alike,  in  correspondence  with  the  nearly  similar  physical 
conditions  of  the  areas;  for  if  we  compare,  for  instance, 
certain  parts  of  South  America  with  parts  of  South 
Africa  or  Australia,  we  see  countries  closely  similar  in 
all  their  physical  conditions,  with  their  inhabitants 
utterly  dissimilar. 

Alternate  Glacial  Periods  in  the  North  and  South. 

But  we  must  return  to  our  more  immediate  subject. 
I  am  convinced  that  Forbes's  view  may  be  largely  ex- 


CHAP.  XII.]      IN  THE  NORTH  AND  SOUTH.  159 

tended.  In  Europe  we  meet  with  the  plainest  evi- 
dence of  the  Glacial  period,  from  the  western  shores 
of  Britain  to  the  Oural  range,  and  southward  to  the 
Pyrenees.  We  may  infer  from  the  frozen  mammals 
and  nature  of  the  mountain  vegetation,  that  Siberia  was 
similarly  affected.  In  the  Lebanon,  according  to  Dr. 
Hooker,  perpetual  snow  formerly  covered  the  central 
axis,  and  fed  glaciers  which  rolled  400  feet  down  the 
valleys.  The  same  observer  has  recently  found  great 
moraines  at  a  low  level  on  the  Atlas  range  in  N.  Africa. 
Along  the  Himalaya,  at  points  900  miles  apart,  glaciers 
have  left  the  marks  of  their  former  low  descent;  and 
in  Sikkim,  Dr.  Hooker  saw  maize  growing  on  ancient 
and  gigantic  moraines.  Southward  of  the  Asiatic  con- 
tinent, on  the  opposite  side  of  the  equator,  we  know, 
from  the  excellent  researches  of  Dr.  J.  Haast  and  Dr. 
Hector,  that  in  New  Zealand  immense  glaciers  formerly 
descended  to  a  low  level;  and  the  same  plants  found 
by  Dr.  Hooker  on  widely  separated  mountains  in  this 
island  tell  the  same  story  of  a  former  cold  period. 
From  facts  communicated  to  me  by  the  Eev.  W.  B. 
Clarke,  it  appears  also  that  there  are  traces  of  former 
glacial  action  on  the  mountains  of  the  south-eastern 
corner  of  Australia. 

Looking  to  America;  in  the  northern  half,  ice-borne 
fragments  of  rock  have  been  observed  on  the  eastern 
side  of  the  continent,  as  far  south  as  lat.  36°-37°,  and 
on  the  shores  of  the  Pacific,  where  the  climate  is  now 
so  different,  as  far  south  as  lat.  46°.  Erratic  boulders 
have,  also, ,  been  noticed  on  the  Rocky  Mountains.  In 
the  Cordillera  of  South  America,  nearly  under  the 
equator,  glaciers  once  extended  far  below  their  present 
level.  In  Central  Chile  I  examined  a  vast  mound  of 


160  ALTERNATE  GLACIAL  PERIODS     [CHAP.  XIL 

detritus  with  great  boulders,  crossing  the  Portillo  valley, 
which  there  can  hardly  be  a  doubt  once  formed  a  huge 
moraine;  and  Mr.  D.  Forbes  informs  me  that  he  found 
in  various  parts  of  the  Cordillera,  from  lat.  13°  to  30°  S., 
at  about  the  height  of  12,000  feet,  deeply-furrowed 
rocks,  resembling  those  with  which  he  was  familiar  in 
Norway,  and  likewise  great  masses  of  detritus,  including 
grooved  pebbles.  Along  this  whole  space  of  the  Cor- 
dillera true  glaciers  do  not  now  exist  even  at  much 
more  considerable  heights.  Farther  south  on  both  sides 
of  the  continent,  from  lat.  41°  to  the  southernmost  ex- 
tremity, we  have  the  clearest  evidence  of  former  glacial 
action,  in  numerous  immense  boulders  transported  far 
from  their  parent  source. 

From  these  several  facts,  namely  from  the  glacial 
action  having  extended  all  round  the  northern  and 
southern  hemispheres — from  the  period  having  been  in 
a  geological  sense  recent  in  both  hemispheres — from  its 
having  lasted  in  both  during  a  great  length  of  time,  as 
may  be  inferred  from  the  amount  of  work  effected — 
and  lastly  from  glaciers  having  recently  descended  to  a 
low  level  along  the  whole  line  of  the  Cordillera,  it  at 
one  time  appeared  to  me  that  we  could  not  avoid  the 
conclusion  that  the  temperature  of  the  whole  world 
had  been  simultaneously  lowered  during  the  Glacial 
period.  But  now  Mr.  Croll,  in  a  series  of  admirable 
memoirs,  has  attempted  to  show  that  a  glacial  con- 
dition of  climate  is  the  result  of  various  physical  causes, 
brought  into  operation  by  an  increase  in  the  eccentricity 
of  the  earth's  orbit.  All  these  causes  tend  towards  the 
same  end;  but  the  most  powerful  appears  to  be  the  in- 
direct influence  of  the  eccentricity  of  the  orbit  upon 
oceanic  currents.  According  to  Mr.  Croll,  cold  periods 


CHAP.  XII.]      IN  THE  NORTH  AND  SOUTH.  1G1 

regularly  occur  every  ten  or  fifteen  thousand  years;  and 
these  at  long  intervals  are  extremely  severe,  owing  to  cer- 
tain contingencies,  of  which  the  most  important,  as  Sir 
C.  Lyell  has  shown,  is  the  relative  position  of  the  land 
and  water.  Mr.  Croll  believes  that  the  last  great  Glacial 
period  occurred  about  240,000  years  ago,  and  endured 
with  slight  alterations  of  climate  for  about  160,000  years. 
With  respect  to  more  ancient  Glacial  periods,  several 
geologists  are  convinced  from  direct  evidence  that  such 
occurred  during  the  Miocene  and  Eocene  formations, 
not  to  mention  still  more  ancient  formations.  But  the 
most  important  result  for  us,  arrived  at  by  Mr.  Croll, 
is  that  whenever  the  northern  hemisphere  passes  through 
a  cold  period  the  temperature  of  the  southern  hemi- 
sphere is  actually  raised,  with  the  winters  rendered  much 
milder,  chiefly  through  changes  in  the  direction  of  the 
ocean-currents.  So  conversely  it  will  be  with  the  north- 
ern hemisphere,  whilst  the  southern  passes  through  a 
Glacial  period.  This  conclusion  throws  so  much  light 
on  geographical  distribution  that  I  am  strongly  inclined 
to  trust  in  it;  but  I  will  first  give  the  facts,  which 
demand  an  explanation. 

In  South  America,  Dr.  Hooker  has  shown  that  be- 
sides many  closely  allied  species,  between  forty  and 
fifty  of  the  flowering  plants  of  Tierra  del  Fuego,  form- 
ing no  inconsiderable  part  of  its  scanty  flora,  are  com- 
mon to  North  America  and  Europe,  enormously  remote 
as  these  areas  in  opposite  hemispheres  are  from  each 
other.  On  the  lofty  mountains  of  equatorial  America 
a  host  of  peculiar  species  belonging  to  European  genera 
occur.  On  the  Organ  mountains  of  Brazil,  some  few 
temperate  European,  some  Antarctic,  and  some  Andean 
genera  were  found  by  Gardner,  which  do  not  exist 


162  ALTERNATE  GLACIAL  PERIODS     [CHAP.  XH. 

in  the  low  intervening  hot  countries.  On  the  Silla  of 
Caraccas,  the  illustrious  Humboldt  long  ago  found 
species  belonging  to  genera  characteristic  of  the  Cordil- 
lera. 

In  Africa,  several  forms  characteristic  of  Europe  and 
some  few  representatives  of  the  flora  of  the  Cape  of 
Good  Hope  occur  on  the  mountains  of  Abyssinia.  At 
the  Cape  of  Good  Hope  a  very  few  European  species,  be- 
lieved not  to  have  been  introduced  by  man,  and  on  the 
mountains  several  representative  European  forms  are 
found,  which  have  not  been  discovered  in  the  inter- 
tropical  parts  of  Africa.  Dr.  Hooker  has  also  lately 
shown  that  several  of  the  plants  living  on  the  upper  parts 
of  the  lofty  island  of  Fernando  Po  and  on  the  neigh- 
bouring Cameroon  mountains,  in  the  Gulf  of  Guinea, 
are  closely  related  to  those  on  the  mountains  of  Abys- 
sinia, and  likewise  to  those  of  temperate  Europe.  It 
now  also  appears,  as  I  hear  from  Dr.  Hooker,  that  some 
of  these  same  temperate  plants  have  been  discovered 
by  the  Rev.  R.  T.  Lowe  on  the  mountains  of  the  Cape 
Verde  islands.  This  extension  of  the  same  temper- 
ate forms,  almost  under  the  equator,  across  the  whole 
continent  of  Africa  and  to  the  mountains  of  the  Cape 
Verde  archipelago,  is  one  of  the  most  astonishing  facts 
ever  recorded  in  the  distribution  of  plants. 

On  the  Himalaya,  and  on  the  isolated  mountain- 
ranges  of  the  peninsula  of  India,  on  the  heights  of 
Ceylon,  and  on  the  volcanic  cones  of  Java,  many  plants 
occur,  either  identically  the  same  or  representing  each 
other,  and  at  the  same  time  representing  plants  of 
Europe,  not  found  in  the  intervening  hot  lowlands. 
A  list  of  the  genera  of  plants  collected  on  the  loftier 
peaks  of  Java,  raises  a  picture  of  a  collection  made  on 


CHAP.  XIL]      IN  THE  NORTH  AND  SOUTH.  163 

a  hillock  in  Europe!  Still  more  striking  is  the  fact 
that  peculiar  Australian  forms  are  represented  by  cer- 
tain plants  growing  on  the  summits  of  the  mountains 
of  Borneo.  Some  of  these  Australian  forms,  as  I  hear 
from  Dr.  Hooker,  extend  along  the  heights  of  the 
peninsula  of  Malacca,  and  are  thinly  scattered  on  the 
one  hand  over  India,  and  on  the  other  hand  as  far  north 
as  Japan. 

On  the  southern  mountains  of  Australia,  Dr.  F. 
Miiller  has  discovered  several  European  species;  other 
species,  not  introduced  by  man,  occur  on  the  lowlands; 
and  a  long  list  can  be  given,  as  I  am  informed  by  Dr. 
Hooker,  of  European  genera,  found  in  Australia,  but 
not  in  the  intermediate  torrid  regions.  In  the  admir- 
able '  Introduction  to  the  Flora  of  New  Zealand/  by  Dr. 
Hooker,  analogous  and  striking  facts  are  given  in  re- 
gard to  the  plants  of  that  large  island.  Hence  we  see 
that  certain  plants  growing  on  the  more  lofty  moun- 
tains of  the  tropics  in  all  parts  of  the  world,  and  on  the 
temperate  plains  of  the  north  and  south,  are  either  the 
same  species  or  varieties  of  the  same  species.  It  should, 
however,  be  observed  that  these  plants  are  not  strictly 
arctic  forms;  for,  as  Mr.  H.  C.  Watson  has  remarked, 
"in  receding  from  polar  towards  equatorial  latitudes, 
the  Alpine  or  mountain  floras  really  become  less  and 
less  Arctic."  Besides  these  identical  and  closely  allied 
forms,  many  species  inhabiting  the  same  widely  sun- 
dered areas,  belong  to  genera  not  now  found  in  the  inter- 
mediate tropical  lowlands. 

These  brief  remarks  apply  to  plants  alone;  but  some 
few  analogous  facts  could  be  given  in  regard  to  terres- 
trial animals.  In  marine  productions,  similar  cases 
likewise  occur;  as  an  example,  I  may  quote  a  statement 


IGi  ALTERNATE  GLACIAL  PERIODS   [CHAP.  XIL 

by  the  highest  authority,  Prof.  Dana,  that  "  it  is  cer- 
tainly a  wonderful  fact  that  New  Zealand  should  have 
a  closer  resemblance  in  its  Crustacea  to  Great  Britain, 
its  antipode,  than  to  any  other  part  of  the  world."  Sir 
J.  Kichardson,  also,  speaks  of  the  reappearance  on  the 
shores  of  New  Zealand,  Tasmania,  &c.,  of  northern 
forms  of  fish.  Dr.  Hooker  informs  me  that  twenty-five 
species  of  Algae  are  common  to  New  Zealand  and  to 
Europe,  but  have  not  been  found  in  the  intermediate 
tropical  seas. 

From  the  foregoing  facts,  namely,  the  presence  of 
temperate  forms  on  the  highlands  across  the  whole  of 
equatorial  Africa,  and  along  the  Peninsula  of  India,  to 
Ceylon  and  the  Malay  Archipelago,  and  in  a  less  well- 
marked  manner  across  the  wide  expanse  of  tropical 
South  America,  it  appears  almost  certain  that  at  some 
former  period,  no  doubt  during  the  most  severe  part  of 
a  Glacial  period,  the  lowlands  of  these  great  continents 
were  everywhere  tenanted  under  the  equator  by  a  con- 
siderable number  of  temperate  forms.  At  this  period 
the  equatorial  climate  at  the  level  of  the  sea  was  prob- 
ably about  the  same  with  that  now  experienced  at 
the  height  of  from  five  to  six  thousand  feet  under  the 
same  latitude,  or  perhaps  even  rather  cooler.  During 
this,  the  coldest  period,  the  lowlands  under  the  equator 
must  have  been  clothed  with  a  mingled  tropical  and 
temperate  vegetation,  like  that  described  by  Hooker  as 
growing  luxuriantly  at  the  height  of  from  four  to  five 
thousand  feet  on  the  lower  slopes  of  the  Himalaya,  but 
with  perhaps  a  still  greater  preponderance  of  temperate 
forms.  So  again  in  the  mountainous  island  of  Fer- 
nando Po,  in  the  Gulf  of  Guinea,  Mr.  Mann  found  tem- 
perate European  forms  beginning  to  appear  at  the  height 


CHAP.  XII.]     IN  THE  NORTH  AND  SOUTH.  165 

of  about  five  thousand  feet.  On  the  mountains  of 
Panama,  at  the  height  of  only  two  thousand  feet,  Dr. 
Seemann  found  the  vegetation  like  that  of  Mexico, 
"  with  forms  of  the  torrid  zone  harmoniously  blended 
with  those  of  the  temperate." 

Now  let  us  see  whether  Mr.  Croll's  conclusion  that 
when  the  northern  hemisphere  suffered  from  the  ex- 
treme cold  of  the  great  Glacial  period,  the  southern 
hemisphere  was  actually  warmer,  throws  any  clear  light 
on  the  present  apparently  inexplicable  distribution  of 
various  organisms  in  the  temperate  parts  of  both  hemi- 
spheres, and  on  the  mountains  of  the  tropics.  The 
Glacial  period,  as  measured  by  years,  must  have  been 
very  long;  and  when  we  remember  over  what  vast 
spaces  some  naturalised  plants  and  animals  have  spread 
within  a  few  centuries,  this  period  will  have  been  ample 
for  any  amount  of  migration.  As  the  cold  became  more 
and  more  intense,  we  know  that  Arctic  forms  invaded 
the  temperate  regions;  and,  from  the  facts  just  given, 
there  can  hardly  be  a  doubt  that  some  of  the  more  vigor- 
ous, dominant,  and  widest-spreading  temperate  forms  in- 
vaded the  equatorial  lowlands.  The  inhabitants  of 
these  hot  lowlands  would  at  the  same  time  have  migrated 
to  the  tropical  and  subtropical  regions  of  the  south,  for 
the  southern  hemisphere  was  at  this  period  warmer. 
On  the  decline  of  the  Glacial  period,  as  both  hemi- 
spheres gradually  recovered  their  former  temperatures, 
the  northern  temperate  forms  living  on  the  lowlands 
under  the  equator,  would  have  been  driven  to  their 
former  homes  or  have  been  destroyed,  being  replaced 
by  the  equatorial  forms  returning  from  the  south. 
Some,  however,  of  the  northern  temperate  forms  would 
almost  certainly  have  ascended  any  adjoining  high  land, 


166  ALTERNATE  GLACIAL  PERIODS   [CHAP.  XII. 

where,  if  sufficiently  lofty,  they  would  have  long  sur- 
vived like  the  Arctic  forms  on  the  mountains  of  Europe. 
They  might  have  survived,  even  if  the  climate  was  not 
perfectly  fitted  for  them,  for  the  change  of  temperature 
must  have  been  very  slow,  and  plants  undoubtedly  pos- 
sess a  certain  capacity  for  acclimatisation,  as  shown  by 
their  transmitting  to  their  offspring  different  consti- 
tutional powers  of  resisting  heat  and  cold. 

In  the  regular  course  of  events  the  southern  hemi- 
sphere would  in  its  turn  be  subjected  to  a  severe  Glacial 
period,  with  the  northern  hemisphere  rendered  warmer; 
and  then  the  southern  temperate  forms  would  invade 
the  equatorial  lowlands.  The  northern  forms  which 
had  before  been  left  on  the  mountains  would  now  de- 
scend and  mingle  with  the  southern  forms.  These 
latter,  when  the  warmth  returned,  would  return  to  their 
former  homes,  leaving  some  few  species  on  the  moun- 
tains, and  carrying  southward  with  them  some  of  the 
northern  temperate  forms  which  had  descended  from 
their  mountain  fastnesses.  Thus,  we  should  have  some 
few  species  identically  the  same  in  the  northern  and 
southern  temperate  zones  and  on  the  mountains  of  the 
intermediate  tropical  regions.  But  the  species  left  dur- 
ing a  long  time  on  these  mountains,  or  in  opposite 
hemispheres,  would  have  to  compete  with  many  new 
forms  and  would  be  exposed  to  somewhat  different 
physical  conditions;  hence  they  would  be  eminently 
liable  to  modification,  and  would  generally  now  exist 
as  varieties  or  as  representative  species;  and  this  is  the 
case.  We  must,  also,  bear  in  mind  the  occurrence  in 
both  hemispheres  of  former  Glacial  periods;  for  these 
will  account,  in  accordance  with  the  same  principles,  for 
the  many  quite  distinct  species  inhabiting  the  same 


CHAP.  XII.]      IX  THE  NORTH  AND  SOUTH.  167 

widely  separated  areas,  and  belonging  to  genera  not  now 
found  in  the  intermediate  torrid  zones. 

It  is  a  remarkable  fact  strongly  insisted  on  by 
Hooker  in  regard  to  America,  and  by  Alph.  de  Can- 
dolle  in  regard  to  Australia,  that  many  more  identical  or 
slightly  modified  species  have  migrated  from  the  north 
to  the  south,  than  in  a  reversed  direction.  We  see, 
however,  a  few  southern  forms  on  the  mountains  of 
Borneo  and  Abyssinia.  I  suspect  that  this  preponder- 
ant migration  from  the  north  to  the  south  is  due  to  the 
greater  extent  of  land  in  the  north,  and  to  the  northern 
forms  having  existed  in  their  own  homes  in  greater 
numbers,  and  having  consequently  been  advanced 
through  natural  selection  and  competition  to  a  higher 
stage  of  perfection,  or  dominating  power,  than  the 
southern  forms.  And  thus,  when  the  two  sets  became 
commingled  in  the  equatorial  regions,  during  the  alter- 
nations of  the  Glacial  periods,  the  northern  forms  were 
the  more  powerful  and  were  able  to  hold  their  places 
on  the  mountains,  and  afterwards  to  migrate  southward 
with  the  southern  forms;  but  not  so  the  southern  in 
regard  to  the  northern  forms.  In  the  same  manner  at 
the  present  day,  we  see  that  very  many  European  pro- 
ductions cover  the  ground  in  La  Plata,  New  Zealand, 
and  to  a  lesser  degree  in  Australia,  and  have  beaten 
the  natives;  whereas  extremely  few  southern  forms  have 
become  naturalised  in  any  part  of  the  northern  hemi- 
sphere, though  hides,  wool,  and  other  objects  likely  to 
carry  seeds  have  been  largely  imported  into  Europe 
during  the  last  two  or  three  centuries  from  La  Plata 
and  during  the  last  forty  or  fifty  years  from  Australia. 
The  Xeilgherrie  mountains  in  India,  however,  offer  a 
partial  exception;  for  here,  as  I  hear  from  Dr.  Hooker, 


168  ALTERNATE  GLACIAL  PERIODS   [CHAP.  XIL 

Australian  forms  are  rapidly  sowing  themselves  and  be- 
coming naturalised.  Before  the  last  great  Glacial 
period,  no  doubt  the  intertropical  mountains  were 
stocked  with  endemic  Alpine  forms;  but  these  have  al- 
most everywhere  yielded  to  the  more  dominant  forms 
generated  in  the  larger  areas  and  more  efficient  work- 
shops of  the  north.  In  many  islands  the  native  pro- 
ductions are  nearly  equalled,  or  .  even  outnumbered, 
by  those  which  have  become  naturalised;  and  this  is 
the  first  stage  towards  their  extinction.  Mountains  are 
islands  on  the  land,  and  their  inhabitants  have  yielded 
to  those  produced  within  the  larger  areas  of  the  north, 
just  in  the  same  way  as  the  inhabitants  of  real  islands 
have  everywhere  yielded  and  are  still  yielding  to  con- 
tinental forms  naturalised  through  man's  agency. 

The  same  principles  apply  to  the  distribution  of  ter- 
restrial animals  and  of  marine  productions,  in  the  north- 
ern and  southern  temperate  zones,  and  on  the  inter- 
tropical  mountains.  When,  during  the  height  of  the 
Glacial  period,  the  ocean-currents  were  widely  differ- 
ent to  what  they  now  are,  some  of  the  inhabitants  of 
the  temperate  seas  might  have  reached  the  equator;  of 
these  a  few  would  perhaps  at  once  be  able  to  migrate 
southward,  by  keeping  to  the  cooler  currents,  whilst 
others  might  remain  and  survive  in  the  colder  depths 
until  the  southern  hemisphere  was  in  its  turn  subjected 
to  a  glacial  climate  and  permitted  their  further  progress; 
in  nearly  the  same  manner  as,  according  to  Forbes,  iso- 
lated spaces  inhabited  by  Arctic  productions  exist  to 
the  present  day  in  the  deeper  parts  of  the  northern 
temperate  seas. 

I  am  far  from  supposing  that  all  the  difficulties  in 
regard  to  the  distribution  and  affinities  of  the  identical 


CHAP.  XII.]      IN  THE  NORTH  AND  SOUTH.  169 

and  allied  species,  which  noAV  live  so  widely  separated 
in  the  north  and  south,  and  sometimes  on  the  inter- 
mediate mountain-ranges,  are  removed  on  the  views 
above  given.  The  exact  lines  of  migration  cannot  be 
indicated.  We  cannot  say  why  certain  species  and  not 
others  have  migrated;  why  certain  species  have  been 
modified  and  have  given  rise  to  new  forms,  whilst  others 
have  remained  unaltered.  We  cannot  hope  to  explain 
such  facts,  until  we  can  say  why  one  species  and  not 
another  becomes  naturalised  by  man's  agency  in  a 
foreign  land;  why  one  species  ranges  twice  or  thrice  as 
far,  and  is  twice  or  thrice  as  common,  as  another  species 
within  their  own  homes. 

Various  special  difficulties  also  remain  to  be  solved; 
for  instance,  the  occurrence,  as  shown  by  Dr.  Hooker,  of 
,the  same  plants  at  points  so  enormously  remote  as  Ker- 
guelen  Land,  New  Zealand,  and  Fuegia;  but  icebergs, 
as  suggested  by  Lyell,  may  have  been  concerned  in  their 
dispersal.  The  existence  at  these  and  other  distant 
points  of  the  southern  hemisphere,  of  species,  which, 
though  distinct,  belong  to  genera  exclusively  confined 
to  the  south,  is  a  more  remarkable  case.  Some  of  these 
species  are  so  distinct,  that  we  cannot  suppose  that  there 
has  been  time  since  the  commencement  of  the  last  Gla- 
cial period  for  their  migration  and  subsequent  modi- 
fication to  the  necessary  degree.  The  facts  seem  to 
indicate  that  distinct  species  belonging  to  the  same 
genera  have  migrated  in  radiating  lines  from  a  common 
centre;  and  I  am  inclined  to  look  in  the  southern,  as  in 
the  northern  hemisphere,  to  a  former  and  warmer 
period,  before  the  commencement  of  the  last  Glacial 
period,  when  the  Antarctic  lands,  now  covered  with  ice, 
supported  a  highly  peculiar  and  isolated  flora.  It  may 
87 


170  ALTERNATE  GLACIAL  PERIODS.  [CHAP.  XII. 

be  suspected  that  before  this  flora  was  exterminated 
during  the  last  Glacial  epoch,  a  few  forms  had  been  al- 
ready widely  dispersed  to  various  points  of  the  southern 
hemisphere  by  occasional  means  of  transport,  and  by  the 
aid  as  halting-places,  of  now  sunken  islands.  Thus  the 
southern  shores  of  America,  Australia,  and  New  Zealand 
may  have  become  slightly  tinted  by  the  same  peculiar 
forms  of  life. 

Sir  C.  Lyell  in  a  striking  passage  has  speculated,  in 
language  almost  identical  with  mine,  on  the  effects  of 
great  alterations  of  climate  throughout  the  world  on 
geographical  distribution.  And  we  have  now  seen  that 
Mr.  Croll's  conclusion  that  successive  Glacial  periods  in 
the  one  hemisphere  coincide  with  warmer  periods  in  the 
opposite  hemisphere,  together  with  the  admission  of  the 
slow  modification  of  species,  explains  a  multitude  of  facts 
in  the  distribution  of  the  same  and  of  the  allied  forms 
of  life  in  all  parts  of  the  globe.  The  living  waters  have 
flowed  during  one  period  from  the  north  and  during 
another  from  the  south,  and  in  both  cases  have  reached 
the  equator;  but  the  stream  of  life  has  flowed  with 
greater  force  from  the  north  than  in  the  opposite  direc- 
tion, and  has  consequently  more  freely  inundated  the 
south.  As  the  tide  leaves  its  drift  in  horizontal  lines, 
rising  higher  on  the  shores  where  the  tide  rises  highest, 
so  have  the  living  waters  left  their  living  drift  on  our 
mountain  summits,  in  a  line  gently  rising  from  the 
Arctic  lowlands  to  a  great  altitude  under  the  equator. 
The  various  beings  thus  left  stranded  may  be  compared 
with  savage  races  of  man,  driven  up  and  surviving  in 
the  mountain  fastnesses  of  almost  every  land,  which 
serve  as  a  record,  full  of  interest  to  us,  of  the  former 
inhabitants  of  the  surrounding  lowlands. 


CHAP.  XIII.]    FRESH-WATER  PRODUCTIONS.  171 


CHAPTER    XIII. 

GEOGRAPHICAL   DISTRIBUTION — continued. 

Distribution  of  fresh-water  productions — On  the  inhabitants  of 
oceanic  islands — Absence  of  Batrachians  and  of  terrestrial  Mam- 
mals—On the  relation  of  the  inhabitants  of  islands  to  those  of 
the  nearest  mainland— On  colonisation  from  the  nearest  source 
•with  subsequent  modification — Summary  of  the  last  and  present 
chapter. 

Fresh-water   Productions. 

As  lakes  and  river-systems  are  separated  from  each 
other  by  barriers  of  land,  it  might  have  been  thought 
that  fresh-water  productions  would  not  have  ranged 
widely  within  the  same  country,  and  as  the  sea  'is  ap- 
parently a  still  more  formidable  barrier,  that  they  would 
never  have  extended  to  distant  countries.  But  the 
case  is  exactly  the  reverse.  Not  only  have  many  fresh- 
water species,  belonging  to  different  classes,  an  enor- 
mous range,  but  allied  species  prevail  in  a  remarkable 
manner  throughout  the  world.  When  first  collecting 
in  the  fresh  waters  of  Brazil,  I  well  remember  feeling 
much  surprise  at  the  similarity  of  the  fresh-water  in- 
sects, shells,  &c.,  and  at  the  dissimilarity  of  the  sur- 
rounding terrestrial  beings,  compared  with  those  of 
Britain. 

But  the  wide  ranging  power  of  fresh-water  produc- 
tions can,  I  think,  in  most  cases  be  explained  by  their 
having  become  fitted,  in  a  manner  highly  useful  to 


172  FRESH-WATER  PRODUCTIONS.    [CHAP.  XIII. 

them,  for  short  and  frequent  migrations  from  pond  to 
pond,  or  from  stream  to  stream,  within  their  own  coun- 
tries; and  liability  to  wide  dispersal  would  follow  from 
this  capacity  as  an  almost  necessary  consequence.  We 
can  here  consider  only  a  few  cases;  of  these,  some  of  the 
most  difficult  to  explain  are  presented  by  fish.  It  was 
formerly  believed  that  the  same  fresh-water  species 
never  existed  on  two  continents  distant  from  each  other. 
But  Dr.  Gunther  has  lately  shown  that  the  Galaxias 
attenuatus  inhabits  Tasmania,  New  Zealand,  the  Falk- 
land Islands,  and  the  mainland  of  South  America.  This 
is  a  wonderful  case,  and  probably  indicates  dispersal 
from  an  Antarctic  centre  during  a  former  warm  period. 
This  case,  however,  is  rendered  in  some  degree  less 
surprising  by  the  species  of  this  genus  having  the 
power  of  crossing  by  some  unknown  means  considerable 
spaces  of  open  ocean:  thus  there  is  one  species  common 
to  New  Zealand  and  to  the  Auckland  Islands,  though 
separated  by  a  distance  of  about  230  miles.  On  the  same 
continent  fresh-water  fish  often  range  widely,  and  as  if 
capriciously;  for  in  two  adjoining  river-systems  some  of 
the  species  may  be  the  same,  and  some  wholly  different. 
It  is  probable  that  they  are  occasionally  transported 
by  what  may  be  called  accidental  means.  Thus  fishes 
still  alive  are  not  very  rarely  dropped  at  distant  points 
by  whirlwinds;  and  it  is  known  that  the  ova  retain 
their  vitality  for  a  considerable  time  after  removal  from 
the  water.  Their  dispersal  may,  however,  be  mainly 
attributed  to  changes  in  the  level  of  the  land  within  the 
recent  period,  causing  rivers  to  flow  into  each  other. 
Instances,  also,  could  be  given  of  this  having  occurred 
during"  floods,  without  any  change  of  level.  The  wide 
difference  of  the  fish  on  the  opposite  sides  of  most 


CHAP.  XIII.]    FRESH-WATER  PRODUCTIONS.  173 

mountain-ranges,  which  are  continuous,  and  which  con- 
sequently must  from  an  early  period  have  completely 
prevented  the  inosculation  of  the  river-systems  on  the 
two  sides,  leads  to  the  same  conclusion.  Some  fresh- 
water fish  belong  to  very  ancient  forms,  and  in  such 
cases  there  will  have  been  ample  time  for  great  geo- 
graphical changes,  and  consequently  time  and  means  for 
much  migration.  Moreover,  Dr.  Giinther  has  recently 
been  led  by  several  considerations  to  infer  that  with 
fishes  the  same  forms  have  a  long  endurance.  Salt- 
water fish  can  with  care  be  slowly  accustomed  to  live  in 
fresh  water;  and,  according  to  Valenciennes,  there  is 
hardly  a  single  group  of  which  all  the  members  are  con- 
fined to  fresh  water,  so  that  a  marine  species  belonging 
to  a  fresh-water  group  might  travel  far  along  the  shores 
of  the  sea,  and  could,  it  is  probable,  become  adapted 
without  much  difficulty  to  the  fresh  waters  of  a  distant 
land. 

Some  species  of  fresh-water  shells  have  very  wide 
ranges,  and  allied  species  which,  on  our  theory,  are  de- 
scended from  a  common  parent,  and  must  have  pro- 
ceeded from  a  single  source,  prevail  throughout  the 
world.  Their  distribution  at  first  perplexed  me  much, 
as  their  ova  are  not  likely  to  be  transported  by  birds; 
and  the  ova,  as  well  as  the  adults,  are  immediately 
killed  by  sea-water.  I  could  not  even  understand  how 
some  naturalised  species  have  spread  rapidly  through- 
out the  same  country.  But  two  facts,  which  I  have  ob- 
served— and  many  others  no  doubt  will  be  discovered — 
throw  some  light  on  this  subject.  When  ducks  sudden- 
ly emerge  from  a  pond  covered  with  duck-weed,  I  have 
twice  seen  these  little  plants  adhering  to  their  backs; 
and  it  has  happened  to  me,  in  removing  a  little  duck- 


174:  FRESH-WATER  PRODUCTIONS.    [CHAP.  XUI. 

weed  from  one  aquarium  to  another,  that  I  have  unin- 
tentionally stocked  the  one  with  fresh-water  shells  from 
the  other.  But  another  agency  is  perhaps  more  effec- 
tual: I  suspended  the  feet  of  a  duck  in  an  aquarium, 
where  many  ova  of  fresh- water  shells  were  hatching; 
and  I  found  that  numbers  of  the  extremely  minute  and 
just-hatched  shells  crawled  on  the  feet,  and  clung  to 
them  so  firmly  that  when  taken  out  of  the  water  they 
could  not  be  jarred  off,  though  at  a  somewhat  more  ad- 
vanced age  they  would  voluntarily  drop  off.  These 
just-hatched  molluscs,  though  aquatic  in  their  nature, 
survived  on  the  duck's  feet,  in  damp  air,  from  twelve  to 
twenty  hours;  and  in  this  length  of  time  a  duck  or 
heron  might  fly  at  least  six  or  seven  hundred  miles,  and 
if  blown  across  the  sea  to  an  oceanic  island,  or  to  any 
other  distant  point,  would  be  sure  to  alight  on  a  pool 
or  rivulet.  Sir  Charles  Lyell  informs  me  that  a  Dytis- 
cus  has  been  caught  with  an  Ancylus  (a  fresh-water 
shell  like  a  limpet)  firmly  adhering  to  it;  and  a  water- 
beetle  of  the  same  family,  a  Colymbetes,  once  flew  on 
board  the  '  Beagle/  when  forty-five  miles  distant  from 
the  nearest  land:  how  much  farther  it  might  have  been 
blown  by  a  favouring  gale  no  one  can  tell. 

With  respect  to  plants,  it  has  long  been  known  what 
enormous  ranges  many  fresh-water,  and  even  marsh 
species,  have,  both  over  continents  and  to  the  most  re- 
mote oceanic  islands.  This  is  strikingly  illustrated,  ac- 
cording to  Alph.  de  Candolle,  in  those  large  groups  of 
terrestrial  plants,  which  have  very  few  aquatic  members; 
for  the  latter  seem  immediately  to  acquire,  as  if  in  con- 
sequence, a  wide  range.  I  think  favourable  means  of 
dispersal  explain  this  fact.  I  have  before  mentioned 
that  earth  occasionally  adheres  in  some  quantity  to  the 


CHAP.  XIII.]   FRESH-WATER  PRODUCTIONS.  175 

feet  and  beaks  of  birds.  Wading  birds,  which  frequent 
the  muddy  edges  of  ponds,  if  suddenly  flushed,  would  be 
the  most  likely  to  have  muddy  feet.  Birds  of  this  order 
wander  more  than  those  of  any  other;  and  they  are 
occasionally  found  on  the  most  remote  and  barren 
islands  of  the  open  ocean;  they  would  not  be  likely  to 
alight  on  the  surface  of  the  sea,  so  that  any  dirt  on  their 
feet  would  not  be  washed  off;  and  when  gaining  the 
land,  they  would  be  sure  to  fly  to  their  natural  fresh- 
water haunts.  I  do  not  believe  that  botanists  are  aware 
how  charged  the  mud  of  ponds  is  with  seeds;  I  have 
tried  several  little  experiments,  but  will  here  give  only 
the  most  striking  case:  I  took  in  February  three  table- 
spoonfuls  of  mud  from  three  different  points,  be- 
neath water,  on  the  edge  of  a  little  pond:  this  mud 
when  dried  weighed  only  6^  ounces;  I  kept  it  covered 
up  in  my  study  for  six  months,  pulling  up  and  counting 
each  plant  as  it  grew;  the  plants  were  of  many  kinds, 
and  were  altogether  537  in  number;  and  yet  the  viscid 
mud  was  all  contained  in  a  breakfast  cup!  Considering 
these  facts,  I  think  it  would  be  an  inexplicable  cir- 
cumstance if  water-birds  did  not  transport  the  seeds 
of  fresh-water  plants  to  unlocked  ponds  and  streams, 
situated  at  very  distant  points.  The  same  agency  may 
have  come  into  play  with  the  eggs  of  some  of  the  smaller 
fresh-water  animals. 

Other  and  unknown  agencies  probably  have  also 
played  a  part.  I  have  stated  that  fresh-water  fish  eat 
some  kinds  of  seeds,  though  they  reject  many  other 
kinds  after  having  swallowed  them;  even  small  fish 
swallow  seeds  of  moderate  size,  as  of  the  yellow  water- 
lily  and  Potamogeton.  Herons  and  other  birds,  cen- 
tury after  century,  have  gone  on  daily  devouring  fish; 


176  FRESH-WATER  PRODUCTIONS.   [CHAP.  XIII. 

they  then  take  flight  and  go  to  other  waters,  or  are 
blown  across  the  sea;  and  we  have  seen  that  seeds  retain 
their  power  of  germination,  when  rejected  many  hours 
afterwards  in  pellets  or  in  the  excrement.  V«rhen  I  saw 
the  great  size  of  the  seeds  of  that  fine  water-lily,  the  Ne- 
lumbium,  and  remembered  Alph.  de  Candolle's  remarks 
on  the  distribution  of  this  plant,!  thought  that  the  means 
of  its  dispersal  must  remain  inexplicable;  but  Audubon 
states  that  he  found  the  seeds  of  the  great  southern 
water-lily  (probably,  according  to  Dr.  Hooker,  the  Ne- 
lumbium  luteum)  in  a  heron's  stomach.  Now  this  bird 
must  often  have  flown  with  its  stomach  thus  well 
stocked  to  distant  ponds,  and  then  getting  a  hearty 
meal  of  fish,  analogy  makes  me  believe  that  it  would 
have  rejected  the  seeds  in  a  pellet  in  a  fit  state  for 
germination. 

In  considering  these  several  means  of  distribution,  it 
should  be  remembered  that  when  a  pond  or  stream  is 
first  formed,  for  instance,  on  a  rising  islet,  it  will  be 
unoccupied;  and  a  single  seed  or  egg  will  have  a  good 
chance  of  succeeding.  Although  there  will  always  be  a 
struggle  for  life  between  the  inhabitants  of  the  same 
pond,  however  few  in  kind,  yet  as  the  number  even  in  a 
well-stocked  pond  is  small  in  comparison  with  the  num- 
ber of  species  inhabiting  an  equal  area  of  land,  the 
competition  between  them  will  probably  be  less  severe 
than  between  terrestrial  species;  consequently  an  in- 
truder from  the  waters  of  a  foreign  country  would  have 
a  better  chance  of  seizing  on  a  new  place,  than  in  the 
case  of  terrestrial  colonists.  We  should  also  remember 
that  many  fresh-water  productions  are  low  in  the  scale 
of  nature,  and  we  have  reason  to  believe  that  such  be- 
ings become  modified  more  slowly  than  the  high;  and 


CHAP.  XIII.]  INHABITANTS  OF  OCEANIC  ISLANDS.     177 

this  will  give  time  for  the  migration  of  aquatic  species. 
We  should  not  forget  the  probability  of  many  fresh- 
water forms  having  formerly  ranged  continuously  over 
immense  areas,  and  then  having  become  extinct  at  in- 
termediate points.  But  the  wide  distribution  of  fresh- 
water plants  and  of  the  lower  animals,  whether  retain- 
ing the  same  identical  form  or  in  some  degree  modified, 
apparently  depends  in  main  part  on  the  wide  dis- 
persal of  their  seeds  and  eggs  by  animals,  more  es- 
pecially by  fresh-water  birds,  which  have  great  powers 
of  flight,  and  naturally  travel  from  one  piece  of  water  to 
another. 

On  the  Inhabitants  of  Oceanic  Islands. 

We  now  come  to  the  last  of  the  three  classes  of  facts, 
which  I  have  selected  as  presenting  the  greatest  amount 
of  difficulty  with  respect  to  distribution,  on  the  view 
that  not  only  all  the  individuals  of  the  same  species 
have  migrated  from  some  one  area,  but  that  allied 
species,  although  now  inhabiting  the  most  distant 
points,  have  proceeded  from  a  single  area, — the  birth- 
place of  their  early  progenitors.  I  have  already  given 
my  reasons  for  disbelieving  in  continental  extensions 
within  the  period  of  existing  species,  on  so  enormous  a 
scale  that  all  the  many  islands  of  the  several  oceans 
were  thus  stocked  with  their  present  terrestrial  inhabi- 
tants. This  view  removes  many  difficulties,  but  it  does 
not  accord  with  all  the  facts  in  regard  to  the  produc- 
tions of  islands.  In  the  following  remarks  I  shall  not 
confine  myself  to  the  mere  question  of  dispersal,  but 
shall  consider  some  other  cases  bearing  on  the  truth  of 
the  two  theories  of  independent  creation  and  of  descent 
with  modification. 


178     INHABITANTS  OP  OCEANIC  ISLANDS.  [CHAP.  XIII. 

The  species  of  all  kinds  which  inhabit  oceanic  is- 
lands are  few  in  number  compared  with  those  on  equal 
continental  areas:  Alph.  de  Candolle  admits  this  for 
plants,  and  Wollaston  for  insects.  New  Zealand,  for 
instance,  with  its  lofty  mountains  and  diversified  sta- 
tions, extending  over  780  miles  of  latitude,  together 
with  the  outlying  islands  of  Auckland,  Campbell  and 
Chatham,  contain  altogether  only  960  kinds  of  flower- 
ing plants;  if  we  compare  this  moderate  number  with 
the  species  which  swarm  over  equal  areas  in  South- 
western Australia  or  at  the  Cape  of  Good  Hope,  we 
must  admit  that  some  cause,  independently  of  different 
physical  conditions,  has  given  rise  to  so  great  a  differ- 
ence in  number.  Even  the  uniform  county  of  Cam- 
bridge has  847  plants,  and  the  little  islahd  of  Angle- 
sea  764,  but  a  few  ferns  and  a  few  introduced  plants 
are  included  in  these  numbers,  and  the  comparison  in 
some  other  respects  is  not  quite  fair.  We  have  evi- 
dence that  the  barren  island  of  Ascension  aboriginally 
possessed  less  than  half-a-dozen  flowering  plants;  yet 
many  species  have  now  become  naturalised  on  it,  as 
they  have  in  New  Zealand  and  on  every  other  oceanic 
island  which  can  be  named.  In  St.  Helena  there  is 
reason  to  believe  that  the  naturalised  plants  and  ani- 
mals have  nearly  or  quite  exterminated  many  native 
productions.  He  who  admits  the  doctrine  of  the  creation 
of  each  separate  species,  will  have  to  admit  that  a  suffi- 
cient number  of  the  best  adapted  plants  and  animals 
were  not  created  for  oceanic  islands;  for  man  has  unin- 
tentionally stocked  them  far  more  fully  and  perfectly 
than  did  nature. 

Although  in  oceanic  islands  the  species  are  few  in 
number,  the  proportion  of  endemic  kinds  (i.  e.  those 


CHAP.  XIII.]  INHABITANTS  OF  OCEANIC  ISLANDS.     179 

found  nowhere  else  in  the  world)  is  often  extremely 
large.  If  we  compare,  for  instance,  the  number  of 
endemic  land-shells  in  Madeira,  or  of  endemic  birds  in 
the  Galapagos  Archipelago,  with  the  number  found  on 
any  continent,  and  then  compare  the  area  of  the  island 
with  that  of  the  continent,  we  shall  see  that  this  is  true. 
This  fact  might  have  been  theoretically  expected,  for, 
as  already  explained,  species  occasionally  arriving  after 
long  intervals  of  time  in  the  new  and  isolated  district, 
and  having  to  compete  with  new  associates,  would  be 
eminently  liable  to  modification,  and  would  often  pro- 
duce groups  of  modified  descendants.  But  it  by  no 
means  follows  that,  because  in  an  island  nearly  all  the 
species  of  one  class  are  peculiar,  those  of  another  class, 
or  of  another  section  of  the  same  class,  are  peculiar; 
and  this  difference  seems  to  depend  partly  on  the  spe- 
cies which  are  not  modified  having  immigrated  in  a 
body,  so  that  their  mutual  relations  have  not  been  much 
disturbed;  and  partly  on  the  frequent  arrival  of  un- 
modified immigrants  from  the  mother-country,  with 
which  the  insular  forms  have  intercrossed.  It  should 
be  borne  in  mind  that  the  offspring  of  such  crosses 
would  certainly  gain  in  vigour;  so  that  even  an  occasional 
cross  would  produce  more  effect  than  might  have  been 
anticipated.  I  will  give  a  few  illustrations  of  the  fore- 
going remarks:  in  the  Galapagos  Islands  there  are  26 
land-birds;  of  these  21  (or  perhaps  23)  are  peculiar, 
whereas  of  the  11  marine  birds  only  2  are  peculiar;  and 
it  is  obvious  that  marine  birds  could  arrive  at  these  is- 
lands much  more  easily  and  frequently  than  land-birds. 
Bermuda,  on  the  other  hand,  which  lies  at  about  the 
same  distance  from  North  America  as  the  Galapagos 
Islands  do  from  South  America,  and  which  has  a  very 


180     INHABITANTS  OF  OCEANIC  ISLANDS.  [CHAP.  XIH. 

peculiar  soil,  does  not  possess  a  single  endemic  land- 
bird;  and  we  know  from  Mr.  J.  M.  Jones's  admirable 
account  of  Bermuda,  that  very  many  North  American 
birds  occasionally  or  even  frequently  visit  this  island. 
Almost  every  year,  as  I  am  informed  by  Mr.  E.  V. 
Harcourt,  many  European  and  African  birds  are 
blown  to  Madeira;  this  island  is  inhabited  by  99  kinds 
of  which  one  alone  is  peculiar,  though  very  closely 
related  to  a  European  form;  and  three  or  four  other 
species  are  confined  to  this  island  and  to  the  Canaries. 
So  that  the  islands  of  Bermuda  and  Madeira  have 
been  stocked  from  the  neighbouring  continents  with 
birds,  which  for  long  ages  have  there  struggled  to- 
gether, and  have  become  mutually  co-adapted.  Hence 
when  settled  in  their  new  homes,  each  kind  will  have 
been  kept  by  the  others  to  its  proper  place  and  habits, 
and  will  consequently  have  been  but  little  liable  to 
modification.  Any  tendency  to  modification  will  also 
have  been  checked  by  intercrossing  with  the  un- 
modified immigrants,  often  arriving  from  the  mother- 
country.  Madeira  again  is  inhabited  by  a  wonder- 
ful number  of  peculiar  land-shells,  whereas  not  one 
species  of  sea-shell  is  peculiar  to  its  shores:  now,  though 
we  do  not  know  how  sea-shells  are  dispersed,  yet  we 
can  see  that  their  eggs  or  larva?,  perhaps  attached 
to  seaweed  or  floating  timber,  or  to  the  feet  of  wading- 
birds,  might  be  transported  across  three  or  four  hun- 
dred miles  of  open  sea  far  more  easily  than  land-shells. 
The  different  orders  of  insects  inhabiting  Madeira  pre- 
sent nearly  parallel  cases. 

Oceanic  islands  are  sometimes  deficient  in  animals  of 
certain  whole  classes,  and  their  places  are  occupied  by 
other  classes;  thus  in  the  Galapagos  Islands  reptiles,. 


CHAP.  XIII.]  INHABITANTS  OP  OCEANIC  ISLANDS.     181 

and  in  New  Zealand  gigantic  wingless  birds,  take,  or 
recently  took,  the  place  of  mammals.  Although  New 
Zealand  is  here  sp'oken  of  as  an  oceanic  island,  it  is  in 
some  degree  doubtful  whether  it  should  be  so  ranked; 
it  is  of  large  size,  and  is  not  separated  from  Australia 
by  a  profoundly  deep  sea;  from  its  geological  charac- 
ter and  the  direction  of  its  mountain-ranges,  the  Rev. 
\V.  B.  Clarke  has  lately  maintained  that  this  island, 
as  well  as  New  Caledonia,  should  be  considered  as  ap- 
purtenances of  Australia.  Turning  to  plants,  Dr. 
Hooker  has  shown  that  in  the  Galapagos  Islands  the 
proportional  numbers  of  the  different  orders  are  very 
different  from  what  they  are  elsewhere.  All  such  dif- 
ferences in  number,  and  the  absence  of  certain  whole 
groups  of  animals  and  plants,  are  generally  accounted 
for  by  supposed  differences  in  the  physical  conditions 
of  the  islands;  but  this  explanation  is  not  a  little 
doubtful.  Facility  of  immigration  seems  to  have 
been  fully  as  important  as  the  nature  of  the  condi- 
tions. 

Many  remarkable  little  facts  could  be  given  with 
respect  to  the  inhabitants  of  oceanic  islands.  For  in- 
stance, in  certain  islands  not  tenanted  by  a  single  mam- 
mal, some  of  the  endemic  plants  have  beautifully  hooked 
seeds;  yet  few  relations  are  more  manifest  than  that 
hooks  serve  for  the  transportal  of  seeds  in  the  wool  or 
fur  of  quadrupeds.  But  a  hooked  seed  might  be 
carried  to  an  island  by  other  means;  and  the  plant  then 
becoming  modified  would  form  an  endemic  species,  still 
retaining  its  hooks,  which  would  form  a  useless  append- 
age like  the  shrivelled  wings  under  the  soldered  wing- 
covers  of  many  insular  beetles.  Again,  islands  often 
possess  trees  or  bushes  belonging  to  orders  which  else- 


182  ABSENCE  OF  TERRESTRIAL     [CHAP.  XIIL 

where  include  only  herbaceous  species;  now  trees,  as 
Alph.  de  Candolle  has  shown,  generally  have,  what- 
ever the  cause  may  be,  confined  ranges.  Hence  trees 
would  be  little  likely  to  reach  distant  oceanic  islands; 
and  an  herbaceous  plant,  which  had  no  chance  of  suc- 
cessfully competing  with  the  many  fully  developed  trees 
growing  on  a  continent,  might,  when  established  on  an 
island,  gain  an  advantage  over  other  herbaceous  plants 
by  growing  taller  and  taller  and  overtopping  them. 
In  this  case,  natural  selection  would  tend  to  add  to  the 
stature  of  the  plant,  to  whatever  order  it  belonged, 
and  thus  first  convert  it  into  a  bush  and  then  into  a 
tree. 

Absence  of  Batrachians  and  Terrestrial  Mammals  on 
Oceanic  Islands. 

With  respect  to  the  absence  of  whole  orders  of  ani- 
mals on  oceanic  islands,  Bory  St.  Vincent  long  ago 
remarked  that  Batrachians  (frogs,  toads,  newts)  are 
never  found  on  any  of  the  many  islands  with  which  the 
great  oceans  are  studded.  I  have  taken  pains  to  verify 
this  assertion,  and  have  found  it  true,  with  the  ex- 
ception of  New  Zealand,  New  Caledonia,  the  Andaman 
Islands,  and  perhaps  the  Salomon  Islands  and  the  Sey- 
chelles. But  I  have  already  remarked  that  it  is  doubt- 
ful whether  New  Zealand  and  New  Caledonia  ought 
to  be  classed  as  oceanic  islands;  and  this  is  still  more 
doubtful  with  respect  to  the  Andaman  and  Salomon 
groups  and  the  Seychelles.  This  general  absence  of 
frogs,  toads,  and  newts  on  so  many  true  oceanic  islands 
cannot  be  accounted  for  by  their  physical  conditions: 
indeed  it  seems  that  islands  are  peculiarly  fitted  for 
these  animals;  for  frogs  have  been  introduced  into  Ma- 


CHAP.  XIII.]  MAMMALS  ON  OCEANIC  ISLANDS.          183 

deira,  the  Azores,  and  Mauritius,  and  have  multiplied 
so  as  to  become  a  nuisance.  But  as  these  animals  and 
their  spawn  are  immediately  killed  (with  the  excep- 
tion, as  far  as  known,  of  one  Indian  species)  by  sea- 
water,  there  would  be  great  difficulty  in  their  trans- 
portal  across  the  sea,  and  therefore  we  can  see  why 
they  do  not  exist  on  strictly  oceanic  islands.  But 
why,  on  the  theory  of  creation,  they  should  not  have 
been  created  there,  it  would  be  very  difficult  to  ex- 
plain. 

Mammals  offer  another  and  similar  case.  I  have 
carefully  searched  the  oldest  voyages,  and  have  not 
found  a  single  instance,  free  from  doubt,  of  a  terrestrial 
mammal  (excluding  domesticated  animals  kept  by  the 
natives)  inhabiting  an  island  situated  above  300  miles 
from  a  continent  or  great  continental  island;  and  many 
islands  situated  at  a  much  less  distance  are  equally 
barren.  The  Falkland  Islands,  which  are  inhabited  by 
a  wolf -like  fox,  come  nearest  to  an  exception;  but  this 
group  cannot  be  considered  as  oceanic,  as  it  lies  on  a 
bank  in  connection  with  the  mainland  at  the  distance 
of  about  280  miles;  moreover,  icebergs  formerly  brought 
boulders  to  its  western  shores,  and  they  may  have  for- 
merly transported  foxes,  as  now  frequently  happens  in 
the  arctic  regions.  Yet  it  cannot  be  said  that  small 
islands  will  not  support  at  least  small  mammals,  for 
they  occur  in  many  parts  of  the  world  on  very  small 
islands,  when  lying  close  to  a  continent;  and  hardly  an 
island  can  be  named  on  which  our  smaller  quadrupeds 
have  not  become  naturalised  and  greatly  multiplied. 
It  cannot  be  said,  on  the  ordinary  view  of  creation,  that 
there  has  not  been  time  for  the  creation  of  mammals; 
many  volcanic  islands  are  sufficiently  ancient,  as  shown 


184:  ABSENCE  OF  TERRESTRIAL      [CHAP.  XIII. 

by  the  stupendous  degradation  which  they  have  suffered, 
and  by  their  tertiary  strata:  there  has  also  been  time 
for  the  production  of  endemic  species  belonging  to 
other  classes;  and  on  continents  it  is  known  that 
new  species  of  mammals  appear  and  disappear  at  a 
quicker  rate  than  other  and  lower  animals.  Although 
terrestrial  mammals  do  not  occur  on  oceanic  islands, 
aerial  mammals  do  occur  on  almost  every  island. 
New  Zealand  possesses  two  bats  found  nowhere  else 
in  the  world:  Norfolk  Island,  the  Viti  Archipelago,  the 
Bonin  Islands,  the  Caroline  and  Marianne  Archipela- 
goes, and  Mauritius,  all  possess  their  peculiar  bats. 
Why,  it  may  be  asked,  has  the  supposed  creative  force 
produced  bats  and  no  other  mammals  on  remote  is- 
lands? On  my  view  this  question  can  easily  be  an- 
swered; for  no  terrestrial  mammal  can  be  transported 
across  a  wide  space  of  sea,  but  bats  can  fly  across. 
Bats  have  been  seen  wandering  by  day  far  over  the 
Atlantic  Ocean;  and  two  North  American  species 
either  regularly  or  occasionally  visit  Bermuda,  at 
the  distance  of  600  miles  from  the  mainland.  I  hear 
from  Mr.  Tomes,  who  has  specially  studied  this 
family,  that  many  species  have  enormous  ranges, 
and  are  found  on  continents  and  on  far  distant  is- 
lands. Hence  we  have  only  to  suppose  that  such 
wandering  species  have  been  modified  in  their  new 
homes  in  relation  to  their  new  position,  and  we  can 
understand  the  presence  of  endemic  bats  on  oceanic 
islands,  with  the  absence  of  all  other  terrestrial  mam- 
mals. 

Another  interesting  relation  exists,  namely  between 
the  depth  of  the  sea  separating  islands  from  each  other 
or  from  the  nearest  continent,  and  the  degree  of  affinity 


CHAP.  XIII].  MAMMALS  ON  OCEANIC  ISLANDS.  185 

of  their  mammalian  inhabitants.  Mr.  Windsor  Earl 
has  made  some  striking  observations  on  this  head,  since 
greatly  extended  by  Mr.  Wallace's  admirable  researches, 
in  regard  to  the  great  Malay  Archipelago,  which  is 
traversed  near  Celebes  by  a  space  of  deep  ocean,  and 
this  separates  two  widely  distinct  mammalian  faunas. 
On  either  side  the  islands  stand  on  a  moderately  shal- 
low submarine  bank,  and  these  islands  are  inhabited  by 
the  same  or  by  closely  allied  quadrupeds.  I  have  not  as 
yet  had  time  to  follow  up  this  subject  in  all  quarters  of 
the  world;  but  as  far  as  I  have  gone,  the  relation  holds 
good.  For  instance,  Britain  is  separated  by  a  shallow 
channel  from  Europe,  and  the  mammals  are  the  same 
on  both  sides;  and  so  it  is  with  all  the  islands  near  the 
shores  of  Australia.  The  West  Indian  Islands,  on  the 
other  hand,  stand  on  a  deeply  submerged  bank,  nearly 
1000  fathoms  in  depth,  and  here  we  find  American 
forms,  but  the  species  and  even  the  genera  are  quite 
distinct.  As  the  amount  of  modification  which  animals 
of  all  kinds  undergo  partly  depends  on  the  lapse  of 
time,  and  as  the  islands  which  are  separated  from  each 
other  or  from  the  mainland  by  shallow  channels,  are 
more  likely  to  have  been  continuously  united  within  a 
recent  period  than  the  islands  separated  by  deeper  chan- 
nels, we  can  understand  how  it  is  that  a  relation  exists 
between  the  depth  of  the  sea  separating  two  mammalian 
faunas,  and  the  degree  of  their  afiinity, — a  relation 
which  is  quite  inexplicable  on  the  theory  of  independ- 
ent acts  of  creation. 

The  foregoing  statements  in  regard  to  the  inhabi- 
tants of  oceanic  islands, — namely,  the  fewness  of  the 
species,  with  a  large  proportion  consisting  of  endemic 
forms — the  members  of  certain  groups,  but  not  those  of 


186  ABSENCE  OF  TERRESTRIAL      [CHAP.  XIII. 

other  groups  in  the  same  class,  having  been  modified — 
the  absence  of  certain  whole  orders,  as  of  batrachians 
and  of  terrestrial  mammals,  notwithstanding  the  pres- 
ence of  aerial  bats, — the  singular  proportions  of  certain 
orders  of  plants, — herbaceous  forms  having  been  de- 
veloped into  trees,  &c., — seem  to  me  to  accord  better 
with  the  belief  in  the  efficiency  of  occasional  means  of 
transport,  carried  on  during  a  long  course  of  time,  than 
with  the  belief  in  the  former  connection  of  all  oceanic 
islands  with  the  nearest  continent;  for  on  this  latter 
view  it  is  probable  that  the  various  classes  would  have 
immigrated  more  uniformly,  and  from  the  species  hav- 
ing entered  in  a  body  their  mutual  relations  would  not 
have  been  much  disturbed,  and  consequently  they  would 
either  have  not  been  modified,  or  all  the  species  in  a 
more  equable  manner. 

I  do  not  deny  that  there  are  many  and  serious  diffi- 
culties in  understanding  how  many  of  the  inhabitants 
of  the  more  remote  islands,  whether  still  retaining  the 
same  specific  form  or  subsequently  modified,  have 
reached  their  present  homes.  But  the  probability  of 
other  islands  having  once  existed  as  halting-places,  of 
which  not  a  wreck  now  remains,  must  not  be  overlooked. 
I  will  specify  one  difficult  case.  Almost  all  oceanic 
islands,  even  the  most  isolated  and  smallest,  are  in- 
habited by  land-shells,  generally  by  endemic  species, 
but  sometimes  by  species  found  elsewhere, — striking 
instances  of  which  have  been  given  by  Dr.  A.  A.  Gould 
in  relation  to  the  Pacific.  Now  it  is  notorious  that 
land-shells  are  easily  killed  by  sea-water;  their  eggs, 
at  least  such  as  I  have  tried,  sink  in  it  and  are  killed. 
Yet  there  must  be  some  unknown,  but  occasionally  effi- 
cient means  for  their  transportal.  Would  the  just- 


CHAP.  XIII.]  MAMMALS  ON  OCEANIC  ISLANDS.          187 

hatched  young  sometimes  adhere  to  the  feet  of  birds 
roosting  on  the  ground,  and  thus  get  transported?  It 
occurred  to  me  that  land-shells,  when  hybernating  and 
having  a  membranous  diaphragm  over  the  mouth  of 
the  shell,  might  be  floated  in  chinks  of  drifted  timber 
across  moderately  wide  arms  of  the  sea.  And  I  find 
that  several  species  in  this  state  withstand  uninjured 
an  immersion  in  sea- water  during  seven  days:  one  shell, 
the  Helix  pomatia,  after  having  been  thus  treated  and 
again  hybernating  was  put  into  sea-water  for  twenty 
days,  and  perfectly  recovered.  During  this  length  of 
time  the  shell  might  have  been  carried  by  a  marine 
current  of  average  swiftness,  to  a  distance  of  660  geo- 
graphical miles.  As  this  Helix  has  a  thick  calcareous 
operculum,  I  removed  it,  and  when  it  had  formed  a 
new  membranous  one,  I  again  immersed  it  for  four- 
teen days  in  sea-water,  and  again  it  recovered  and 
crawled  away.  Baron  Aucapitaine  has  since  tried  simi- 
lar experiments:  he  placed  100  land-shells,  belonging 
to  ten  species,  in  a  box  pierced  with  holes,  and  im- 
mersed it  for  a  fortnight  in  the  sea.  Out  of  the  hun- 
dred shells,  twenty-seven  recovered.  The  presence  of 
an  operculum  seems  to  have  been  of  importance,  as 
out  of  twelve  specimens  of  Cyclostoma  elegans,  which 
is  thus  furnished,  eleven  revived.  It  is  remarkable, 
seeing  how  well  the  Helix  pomatia  resisted  with  me  the 
salt-water,  that  not  one  of  fifty-four  specimens  be- 
longing to  four  other  species  of  Helix  tried  by  Aucapi- 
taine, recovered.  It  is,  however,  not  at  all  probable 
that  land-shells  have  often  been  thus  transported;  the 
feet  of  birds  offer  a  more  probable  method. 


188  RELATIONS  OF  THE  INHABITANTS  OF  [CHAP.  XIIL 

On  the  Relations  of  the  Inhabitants  of  Islands  to  those  of 
the  nearest  Mainland. 

The  most  striking  and  important  fact  for  us  is  the 
affinity  of  the  species  which  inhabit  islands  to  those  of 
the  nearest  mainland,  without  being  actually  the  same. 
Numerous  instances  could  be  given.  The  Galapagos 
Archipelago,  situated  under  the  equator,  lies  at  the 
distance  of  between  500  and  600  miles  from  the  shores 
of  South  America.  Here  almost  every  product  of  the 
land  and  of  the  water  bears  the  unmistakable  stamp  of 
the  American  continent.  There  are  twenty-six  land- 
birds;  of  these,  twenty-one,  or  perhaps  twenty-three  are 
ranked  as  distinct  species,  and  would  commonly  be 
assumed  to  have  been  here  created;  yet  the  close  affinity 
of  most  of  these  birds  to  American  species  is  manifest 
in  every  character,  in  their  habits,  gestures,  and  tones 
of  voice.  So  it  is  with  the  other  animals,  and  with  a 
large  proportion  of  the  plants,  as  shown  by  Dr.  Hooker 
in  his  admirable  Flora  of  this  archipelago.  The  natu- 
ralist, looking  at  the  inhabitants  of  these  volcanic  is- 
lands in  the  Pacific,  distant  several  hundred  miles  from 
the  continent,  feels  that  he  is  standing  on  American 
land.  Why  should  this  be  so?  why  should  the  species 
which  are  supposed  to  have  been  created  in  the  Gala- 
pagos Archipelago,  and  nowhere  else,  bear  so  plainly 
the  stamp  of  affinity  to  those  created  in  America?  There 
is  nothing  in  the  conditions  of  life,  in  the  geological 
nature  of  the  islands,  in  their  height  or  climate,  or  in 
the  proportions  in  which  the  several  classes  are  asso- 
ciated together,  which  closely  resembles  the  conditions 
of  the  South  American  coast:  in  fact,  there  is  a  con- 
siderable dissimilarity  in  all  these  respects.  On  the 


CHAP.  XIII.]  ISLANDS  TO  THOSE  OF  THE  MAINLAND.  189 

other  hand,  there  is  a  considerable  degree  of  resem- 
blance in  the  volcanic  nature  of  the  soil,  in  the  climate, 
height,  and  size  of  the  islands,  between  the  Galapagos 
and  Cape  Verde  Archipelagoes:  but  what  an  entire  and 
absolute  difference  in  their  inhabitants!  The  inhabi- 
tants of  the  Cape  Verde  Islands  are  related  to  those  of 
Africa,  like  those  of  the  Galapagos  to  America.  Facts 
such  as  these,  admit  of  no  sort  of  explanation  on  the 
ordinary  view  of  independent  creation;  whereas  on  the 
view  here  maintained,  it  is  obvious  that  the  Galapagos 
Islands  would  be  likely  to  receive  colonists  from  Amer- 
ica, whether  by  occasional  means  of  transport  or  (though 
I  do  not  believe  in  this  doctrine)  by  formerly  continu- 
ous land,  and  the  Cape  Verde  Islands  from  Africa; 
such  colonists  would  be  liable  to  modification, — the 
principle  of  inheritance  still  betraying  their  original 
birthplace. 

Many  analogous  facts  could  be  given:  indeed  it  is  an 
almost  universal  rule  that  the  endemic  productions  of 
islands  are  related  to  those  of  the  nearest  continent,  or 
of  the  nearest  large  island.  The  exceptions  are  few, 
and  most  of  them  can  be  explained.  Thus  although 
Kerguelen  Land  stands  nearer  to  Africa  than  to  Amer- 
ica, the  plants  are  related,  and  that  very  closely,  as  we 
know  from  Dr.  Hooker's  account,  to  those  of  America: 
but  on  the  view  that  this  island  has  been  mainly  stocked 
by  seeds  brought  with  earth  and  stones  on  icebergs, 
drifted  by  the  prevailing  currents,  this  anomaly  dis- 
appears. Xew  Zealand  in  its  endemic  planes  is  much 
more  closely  related  to  Australia,  the  nearest  mainland, 
than  to  any  other  region:  and  this  is  what  might  have 
been  expected;  but  it  is  also  plainly  related  to  South 
America,  which,  although  the  next  nearest  continent,  is 


190  RELATIONS  OF  THE  INHABITANTS  OF  [CHAP.  XIII. 

so  enormously  remote,  that  the  fact  becomes  an  anom- 
aly. But  this  difficulty  partially  disappears  on  the 
view  that  New  Zealand,  South  America,  and  the  other 
southern  lands  have  been  stocked  in  part  from  a  nearly 
intermediate  though  distant  point,  namely  from  the  ant- 
arctic islands,  when  they  were  clothed  with  vegetation, 
during  a  warmer  tertiary  period,  before  the  commence- 
ment of  the  last  Glacial  period.  The  affinity,  which 
though  feeble,  I  am  assured  by  Dr.  Hooker  is  real,  be- 
tween the  flora  of  the  south-western  corner  of  Australia 
and  of  the  Cape  of  Good  Hope,  is  a  far  more  remarkable 
case;  but  this  affinity  is  confined  to  the  plants,  and  will, 
no  doubt,  some  day  be  explained. 

The  same  law  which  has  determined  the  relation- 
ship between  the  inhabitants  of  islands  and  the  nearest 
mainland,  is  sometimes  displayed  on  a  small  scale,  but 
in  a  most  interesting  manner,  within  the  limits  of  the 
same  archipelago.  Thus  each  separate  island  of  the 
Galapagos  Archipelago  is  tenanted,  and  the  fact  is  a 
marvellous  one,  by  many  distinct  species;  but  these 
species  are  related  to  each  other  in  a  very  much  closer 
manner  than  to  the  inhabitants  of  the  American  con- 
tinent, or  of  any  other  quarter  of  the  world.  This  is 
what  might  have  been  expected,  for  islands  situated  so 
near  to  each  other  would  almost  necessarily  receive 
immigrants  from  the  same  original  source,  and  from 
each  other.  But  how  is  it  that  many  of  the  immigrants 
have  been  differently  modified,  though  only  in  a  small 
degree,  in  islands  situated  within  sight  of  each  other, 
having  the  same  geological  nature,  the  same  height, 
climate,  &c.?  This  long  appeared  to  me  a  great  diffi- 
culty: but  it  arises  in  chief  part  from  the  deeply-seated 
error  of  considering  the  physical  conditions  of  a  country 


CHAP.  XIII.]  ISLANDS  TO  THOSE  OF  THE  MAINLAND.  191 

as  the  most  important;  whereas  it  cannot  be  disputed 
that  the  nature  of  the  other  species  with  which  each  has 
to  compete,  is  at  least  as  important,  and  generally  a  far 
more  important  element  of  success.  Now  if  we  look  to 
the  species  which  inhabit  the  Galapagos  Archipelago, 
and  are  likewise  found  in  other  parts  of  the  world,  we 
find  that  they  differ  considerably  in  the  several  islands. 
This  difference  might  indeed  have  been  expected  if  the 
islands  had  been  stocked  by  occasional  means  of  trans- 
port— a  seed,  for  instance,  of  one  plant  having  been 
brought  to  one  island,  and  that  of  another  plant  to 
another  island,  though  all  proceeding  from  the  same 
general  source.  Hence,  when  in  former  times  an  im- 
migrant first  settled  on  one  of  the  islands,  or  when  it 
subsequently  spread  from  one  to  another,  it  would  un- 
doubtedly be  exposed  to  different  conditions  in  the 
different  islands,  for  it  would  have  to  compete  with  a 
different  set  of  organisms;  a  plant,  for  instance,  would 
find  the  ground  best  fitted  for  it  occupied  by  somewhat 
different  species  in  the  different  islands,  and  would  be 
exposed  to  the  attacks  of  somewhat  different  enemies. 
If  then  it  varied,  natural  selection  would  probably  fa- 
vour different  varieties  in  the  different  islands.  Some 
species,  however,  might  spread  and  yet  retain  the  same 
character  throughout  the  group,  just  as  we  see  some 
species  spreading  widely  throughout  a  continent  and 
remaining  the  same. 

The  really  surprising  fact  in  this  case  of  the  Gala- 
pagos Archipelago,  and  in  a  lesser  degree  in  some  an- 
alogous cases,  is  that  each  new  species  after  being  formed 
in  any  one  island,  did  not  spread  quickly  to  the  other  is- 
lands. But  the  islands,  though  in  sight  of  each  other, 
are  separated  by  deep  arms  of  the  sea,  in  most  cases 


192  RELATIONS  OF  THE  INHABITANTS  OF  [CHAP.  XUI. 

wider  than  the  British  Channel,  and  there  is  no  reason 
to  suppose  that  they  have  at  any  former  period  been 
continuously  united.  The  currents  of  the  sea  are  rapid 
and  sweep  between  the  islands,  and  gales  of  wind  are 
extraordinarily  rare;  so  that  the  islands  are  far  more 
effectually  separated  from  each  other  than  they  appear 
on  a  map.  Nevertheless  some  of  the  species,  both  of 
those  found  in  other  parts  of  the  world  and  of  those 
confined  to  the  archipelago,  are  common  to  the  several 
islands;  and  we  may  infer  from  their  present  manner 
of  distribution,  that  they  have  spread  from  one  island 
to  the  others.  But  we  often  take,  I  think,  an  erroneous 
view  of  the  probability  of  closely-allied  species  invading 
each  other's  territory,  when  put  into  free  intercom- 
munication. Undoubtedly,  if  one  species  has  any  ad- 
vantage over  another,  it  will  in  a  very  brief  time  wholly 
or  in  part  supplant  it;  but  if  both  are  equally  well  fitted 
for  their  own  places,  both  will  probably  hold  their  sepa- 
rate places  for  almost  any  length  of  time.  Being  famil- 
iar with  the  fact  that  many  species,  naturalised  through 
man's  agency,  have  spread  with  astonishing  rapidity 
over  wide  areas,  we  are  apt  to  infer  that  most  species 
would  thus  spread;  but  we  should  remember  that  the 
species  which  become  naturalised  in  new  countries  are 
not  generally  closely  allied  to  the  aboriginal  inhabi- 
tants, but  are  very  distinct  forms,  belonging  in  a  large 
proportion  of  cases,  as  shown  by  Alph.  de  Candolle,  to 
distinct  genera.  In  the  Galapagos  Archipelago,  many 
even  of  the  birds,  though  so  well  adapted  for  flying 
from  island  to  island,  differ  on  the  different  islands; 
thus  there  are  three  closely-allied  species  of  mocking- 
thrush,  each  confined  to  its  own  island.  Now  let  us 
suppose  the  mocking-thrush  of  Chatham  Island  to  be 


CHAP.  XIII.]  ISLANDS  TO  THOSE  OF  THE  MAINLAND.  193 

blown  to  Charles  Island,  which  has  its  own  mocking- 
thrush;  why  should  it  succeed  in  establishing  itself 
there?  We  may  safely  infer  that  Charles  Island  is 
well  stocked  with  its  own  species,  for  annually  more 
eggs  are  laid  and  young  birds  hatched,  than  can  possibly 
be  reared;  and  we  may  infer  that  the  mocking-thrush 
peculiar  to  Charles's  Island  is  at  least  as  well  fitted  for 
its  home  as  is  the  species  peculiar  to  Chatham  Island. 
Sir  C.  Lyell  and  Mr.  Wollaston  have  communicated  to 
me  a  remarkable  fact  bearing  on  this  subject;  namely, 
that  Madeira  and  the  adjoining  islet  of  Porto  Santo 
possess  many  distinct  but  representative  species  of  land- 
shells,  some  of  which  live  in  crevices  of  stone;  and 
although  large  quantities  of  stone  are  annually  trans- 
ported from  Porto  Santo  to  Madeira,  yet  this  latter 
island  has  not  become  colonised  by  the  Porto  Santo 
species;  nevertheless  both  islands  have  been  colonised 
by  European  land-shells,  which  no  doubt  had  some 
advantage  over  the  indigenous  species.  From  these 
considerations  I  think  we  need  not  greatly  marvel  at 
the  endemic  species  which  inhabit  the  several  islands  of 
the  Galapagos  Archipelago,  not  having  all  spread  from 
island  to  island.  On  the  same  continent,  also,  pre- 
occupation has  probably  played  an  important  part  in 
checking  the  commingling  of  the  species  which  inhabit 
different  districts  with  nearly  the  same  physical  condi- 
tions. Thus,  the  south-east  and  south-west  corners  of 
Australia  have  nearly  the  same  physical  conditions,  and 
are  united  by  continuous  land,  yet  they  are  inhabited 
by  a  vast  number  of  distinct  mammals,  birds,  and  plants; 
so  it  is,  according  to  Mr.  Bates,  with  the  butterflies  and 
other  animals  inhabiting  the  great,  open,  and  continu- 
ous valley  of  the  Amazons. 


194  RELATIONS  OF  THE  INHABITANTS  OF  [CHAP.  XIII. 

The  same  principle  which  governs  the  general  char- 
acter of  the  inhabitants  of  oceanic  islands,  namely,  the 
relation  to  the  source  whence  colonists  could  have  been 
most  easily  derived,  together  with  their  subsequent 
modification,  is  of  the  widest  application  throughout 
nature.  "We  see  this  on  every  mountain-summit,  in 
every  lake  and  marsh.  For  Alpine  species,  excepting 
in  as  far  as  the  same  species  have  become  widely 
spread  during  the  Glacial  epoch,  are  related  to  those 
of  the  surrounding  lowlands;  thus  we  have  in  South 
America,  Alpine  humming-birds,  Alpine  rodents,  Al- 
pine plants,  &c.,  all  strictly  belonging  to  American 
forms;  and  it  is  obvious  that  a  mountain,  as  it  became 
slowly  upheaved,  would  be  colonised  from  the  surround- 
ing lowlands.  So  it  is  with  the  inhabitants  of  lakes 
and  marshes,  excepting  in  so  far  as  great  facility  of 
transport  has  allowed  the  same  forms  to  prevail  through- 
out large  portions  of  the  world.  We  see  this  same  prin- 
ciple in  the  character  of  most  of  the  blind  animals  in- 
habiting the  caves  of  America  and  of  Europe.  Other 
analogous  facts  could  be  given.  It  will,  I  believe,  be 
found  universally  true,  that  wherever  in  two  regions, 
let  them  be  ever  so  distant,  many  closely  allied  or 
representative  species  occur,  there  will  likewise  be  found 
some  identical  species;  and  wherever  many  closely-al- 
lied species  occur,  there  will  be  found  many  forms  which 
some  naturalists  rank  as  distinct  species,  and  others  as 
mere  varieties;  these  doubtful  forms  showing  us  the 
steps  in  the  progress  of  modification. 

The  relation  between  the  power  and  extent  of  mi- 
gration in  certain  species,  either  at  the  present  or  at 
some  former  period,  and  the  existence  at  remote  points 
of  the  world  of  closely-allied  species,  is  shown  in  an- 


CHAP.  XIII.]  ISLANDS  TO  THOSE  OP  THE  MAINLAND.  195 

other  and  more  general  way.  Mr.  Gould  remarked 
to  me  long  ago,  that  in  those  genera  of  birds  which 
range  over  the  world,  many  of  the  species  have  very 
wide  ranges.  I  can  hardly  doubt  that  this  rule  is  gen- 
erally true,  though  difficult  of  proof.  Amongst  mam- 
mals, we  see  it  strikingly  displayed  in  Bats,  and  in  a 
lesser  degree  in  the  Felidae  and  Canidae.  We  see  the 
same  rule  in  the  distribution  of  butterflies  and  beetles. 
So  it  is  with  most  of  the  inhabitants  of  fresh  water, 
for  many  of  the  genera  in  the  most  distinct  classes  range 
over  the  world,  and  many  of  the  species  have  enormous 
ranges.  It  is  not  meant  that  all,  but  that  some  of  the 
species  have  very  wide  ranges  in  the  genera  which  range 
very  widely.  Nor  is  it  meant  that  the  species  in 
euch  genera  have  on  an  average  a  very  wide  range;  for 
this  will  largely  depend  on  how  far  the  process  of  modi- 
fication has  gone;  for  instance,  two  varieties  of  the 
same  species  inhabit  America  and  Europe,  and  thus 
the  species  has  an  immense  range;  but,  if  variation 
were  to  be  carried  a  little  further,  the  two  varieties 
would  be  ranked  as  distinct  species,  and  their  range 
would  be  greatly  reduced.  Still  less  is  it  meant,  that 
species  which  have  the  capacity  of  crossing  barriers  and 
ranging  widely,  as  in  the  case  of  certain  powerfully- 
winged  birds,  will  necessarily  range  widely;  for  we 
should  never  forget  that  to  range  widely  implies  not 
only  the  power  of  crossing  barriers,  but  the  more  im- 
portant power  of  being  victorious  in  distant  lands 
in  the  struggle  for  life  with  foreign  associates.  But 
according  to  the  view  that  all  the  species  of  a  genus, 
though  distributed  to  the  most  remote  points  of 
the  world,  are  descended  from  a  single  progenitor, 
we  ought  to  find,  and  I  believe  as  a  general  rule  we 


196  RELATIONS  OF  THE  INHABITANTS  OF  [CHAP.  XIIL 

do  find,  that  some  at  least  of  the  species  range  very 
widely. 

We  should  bear  in  mind  that  many  genera  in  all 
classes  are  of  ancient  origin,  and  the  species  in  this 
case  will  have  had  ample  time  for  dispersal  and  sub- 
sequent modification.  There  is  also  reason  to  believe 
from  geological  evidence,  that  within  each  great  class 
the  lower  organisms  change  at  a  slower  rate  than  the 
higher;  consequently  they  will  have  had  a  better  chance 
of  ranging  widely  and  of  still  retaining  the  same  spe- 
cific character.  This  fact,  together  with  that  of  the 
seeds  and  eggs  of  most  lowly  organised  forms  being  very 
minute  and  better  fitted  for  distant  transportal,  prob- 
ably accounts  for  a  law  which  has  long  been  observed, 
and  which  has  lately  been  discussed  by  Alph.  de  Can- 
dolle  in  regard  to  plants,  namely,  that  the  lower 
any  group  of  organisms  stands  the  more  widely  it 
ranges. 

The  relations  just  discussed, — namely,  lower  organ- 
isms ranging  more  widely  than  the  higher, — some  of 
the  species  of  widely-ranging  genera  themselves  ranging 
widely, — such  facts,  as  alpine,  lacustrine,  and  marsh 
productions  being  generally  related  to  those  which  live 
on  the  surrounding  low  lands  and  dry  lands, — the 
striking  relationship  between  the  inhabitants  of  islands 
and  those  of  the  nearest  mainland — the  still  closer  re- 
lationship of  the  distinct  inhabitants  of  the  islands  in 
the  same  archipelago — are  inexplicable  on  the  ordinary 
view  of  the  independent  creation  of  each  species,  but 
are  explicable  if  we  admit  colonisation  from  the  nearest 
or  readiest  source,  together  with  the  subsequent  adap- 
tation of  the  colonists  to  their  new  homes. 


CHAP.  XIII.]  ISLANDS  TO  THOSE  OF  THE  MAINLAND.  197 

Summary  of  the  last  and  present  Chapters. 

In  these  chapters  I  have  endeavoured  to  show,  that 
if  we  make  due  allowance  for  our  ignorance  of  the  full 
effects  of  changes  of  climate  and  of  the  level  of  the 
land,  which  have  certainly  occurred  within  the  recent 
period,  and  of  other  changes  which  have  probably  oc- 
curred,— if  we  remember  how  ignorant  we  are  with 
respect  to  the  many  curious  means  of  occasional  trans- 
port,— if  we  bear  in  mind,  and  this  is  a  very  important 
consideration,  how  often  a  species  may  have  ranged 
continuously  over  a  wide  area,  and  then  have  become 
extinct  in  the  intermediate  tracts, — the  difficulty  is  not 
insuperable  in  believing  that  all  the  individuals  of  the 
same  species,  wherever  found,  are  descended  from  com- 
mon parents.  And  we  are  led  to  this  conclusion,  which 
has  been  arrived  at  by  many  naturalists  under  the  desig- 
nation of  single  centres  of  creation,  by  various  gen- 
eral considerations,  more  especially  from  the  impor- 
tance of  barriers  of  all  kinds,  and  from  the  analogical 
distribution  of  sub-genera,  genera,  and  families. 

With  respect  to  distinct  species  belonging  to  the 
same  genus,  which  on  our  theory  have  spread  from  one 
parent-source;  if  we  make  the  same  allowances  as  be- 
fore for  our  ignorance,  and  remember  that  some  forms 
of  life  have  changed  very  slowly,  enormous  periods 
of  time  having  been  thus  granted  for  their  migration, 
the  difficulties  are  far  from  insuperable;  though  in  this 
case,  as  in  that  of  the  individuals  of  the  same  species, 
they  are  often  great. 

As  exemplifying  the  effects  of  climatal  changes  on 
distribution,  I  have  attempted  to  show  how  important 
a  part  the  last  Glacial  period  has  played,  which  affected 


198  SUMMARY  OF  THE  [CHAP.  XIII. 

even  the  equatorial  regions,  and  which,  during  the  al- 
ternations of  the  cold  in  the  north  and  south,  allowed 
the  productions  of  opposite  hemispheres  to  mingle,  and 
left  some  of  them  stranded  on  the  mountain-summits 
in  all  parts  of  the  world.  As  showing  how  diversified 
are  the  means  of  occasional  transport,  I  have  discussed 
at  some  little  length  the  means  of  dispersal  of  fresh- 
water productions. 

If  the  difficulties  be  not  insuperable  in  admitting 
that  in  the  long  course  of  time  all  the  individuals  of 
the  same  species,  and  likewise  of  the  several  species 
belonging  to  the  same  genus,  have  proceeded  from  some 
one  source;  then  all  the  grand  leading  facts  of  geo- 
graphical distribution  are  explicable  on  the  theory 
of  migration,  together  with  subsequent  modification  and 
the  multiplication  of  new  forms.  We  can  thus  under- 
stand the  high  importance  of  barriers,  whether  of  land 
or  water,  in  not  only  separating,  but  in  apparently  form- 
ing the  several  zoological  and  botanical  provinces.  We 
can  thus  understand  the  concentration  of  related  species 
within  the  same  areas;  and  how  it  is  that  under  dif- 
ferent latitudes,  for  instance  in  South  America,  the  in- 
habitants of  the  plains  and  mountains,  of  the  forests, 
marshes,  and  deserts,  are  linked  together  in  so  mysterious 
a  manner,  and  are  likewise  linked  to  the  extinct  beings 
which  formerly  inhabited  the  same  continent.  Bear- 
ing in  mind  that  the  mutual  relation  of  organism  to 
organism  is  of  the  highest  importance,  we  can  see  why 
two  areas  having  nearly  the  same  physical  conditions 
should  often  be  inhabited  by  very  different  forms  of  life; 
for  according  to  the  length  of  time  which  has  elapsed 
since  the  colonists  entered  one  of  the  regions,  or  both; 
according  to  the  nature  of  the  communication  which 


CHAP.  XIII.]  LAST  AND  PRESENT  CHAPTERS.  199 

allowed  certain  forms  and  not  others  to  enter,  either 
in  greater  or  lesser  numbers;  according  or  not,  as 
those  which  entered  happened  to  come  into  more  or  less 
direct  competition  with  each  other  and  with  the 
aborigines;  and  according  as  the  immigrants  were 
capable  of  varying  more  or  less  rapidly,  there  would 
ensue  in  the  two  or  more  regions,  independently  of 
their  physical  conditions,  infinitely  diversified  con- 
ditions of  life, — there  would  be  an  almost  endless 
amount  of  organic  action  and  reaction, — and  we 
should  find  some  groups  of  beings  greatly,  and  some 
only  slightly  modified, — some  developed  in  great  force, 
some  existing  in  scanty  numbers — and  this  we  do  find 
in  the  several  great  geographical  provinces  of  the  world. 
On  these  same  principles  we  can  understand,  as  I 
have  endeavoured  to  show,  why  oceanic  islands  should 
have  few  inhabitants,  but  that  of  these,  a  large  propor- 
tion should  be  endemic  or  peculiar;  and  why,  in  rela- 
tion to  the  means  of  migration,  one  group  of  beings 
should  have  all  its  species  peculiar,  and  another  group, 
even  within  the  same  class,  should  have  all  its  species 
the  same  with  those  in  an  adjoining  quarter  of  the 
world.  We  can  see  why  whole  groups  of  organisms,  as 
batrachians  and  terrestrial  mammals,  should  be  absent 
from  oceanic  islands,  whilst  the  most  isolated  islands 
should  possess  their  own  peculiar  species  of  aerial  mam- 
mals or  bats.  We  can  see  why,  in  islands,  there  should 
be  some  relation  between  the  presence  of  mammals,  in 
a  more  or  less  modified  condition,  and  the  depth  of  the 
sea  between  such  islands  and  the  mainland.  We  can 
clearly  see  why  all  the  inhabitants  of  an  archipelago, 
though  specifically  distinct  on  the  several  islets,  should 
be  closely  related  to  each  other;  and  should  likewise 


200  SUMMARY  OP  THE  [CHAP.  XIII. 

be  related,  but  less  closely,  to  those  of  the  nearest  con- 
tinent, or  other  source  whence  immigrants  might 
have  been  derived.  We  can  see  why,  if  there  exist  very 
closely  allied  or  representative  species  in  two  areas, 
however  distant  from  each  other,  some  identical  species 
will  almost  always  there  be  found. 

As  the  late  Edward  Forbes  often  insisted,  there  is  a 
striking  parallelism  in  the  laws  of  life  throughout  time 
and  space;  the  laws  governing  the  succession  of  forms 
in  past  times  being  nearly  the  same  with  those  govern- 
ing at  the  present  time  the  differences  in  different  areas. 
We  see  this  in  many  facts.  The  endurance  of  each  spe- 
cies and  group  of  species  is  continuous  in  time;  for 
the  apparent  exceptions  to  the  rule  are  so  few,  that 
they  may  fairly  be  attributed  to  our  not  having  as  yet 
discovered  in  an  intermediate  deposit  certain  forms 
which  are  absent  in  it,  but  which  occur  both  above  and 
below:  so  in  space,  it  certainly  is  the  general  rule  that 
the  area  inhabited  by  a  single  species,  or  by  a  group  of 
species,  is  continuous,  and  the  exceptions,  which  are  not 
rare,  may,  as  I  have  attempted  to  show,  be  accounted  for 
by  former  migrations  under  different  circumstances,  or 
through  occasional  means  of  transport,  or  by  the  species 
having  become  extinct  in  the  intermediate  tracts. 
Both  in  time  and  space  species  and  groups  of  species 
have  their  points  of  maximum  development.  Groups  of 
species,  living  during  the  same  period  of  time,  or  liv- 
ing within  the  same  area,  are  often  characterised  by 
trifling  features  in  common,  as  of  sculpture  or  colour. 
In  looking  to  the  long  succession  of  past  ages,  as  in 
looking  to  distant  provinces  throughout  the  world,  we 
find  that  species  in  certain  classes  differ  little  from  each 
other,  whilst  those  in  another  class,  or  only  in  a  different 


CHAP.  XIII.]  LAST  AND  PRESENT  CHAPTERS.  201 

section  of  the  same  order,  differ  greatly  from  each  other. 
In  both  time  and  space  the  lowly  organised  members 
of  each  class  generally  change  less  than  the  highly 
organised;  but  there  are  in  both  cases  marked  excep- 
tions to  the  rule.  According  to  our  theory,  these  sev- 
eral relations  throughout  time  and  space  are  intelli- 
gible; for  whether  we  look  to  the  allied  forms  of  life 
which  have  changed  during  successive  ages,  or  to  those 
which  have  changed  after  having  migrated  into  distant 
quarters,  in  both  cases  they  are  connected  by  the  same 
bond  of  ordinary  generation;  in  both  cases  the  laws  of 
variation  have  been  the  same,  and  modifications 
have  been  accumulated  by  the  same  means  of  natural 
selection. 


202  CLASSIFICATION.  [CHAP.  XIV. 


CHAPTER    XIV. 

MUTUAL      AFFINITIES       OF       ORGANIC       BEINGS:        MOR- 
PHOLOGY:  EMBRYOLOGY:    RUDIMENTARY  ORGANS. 

CLASSIFICATION,  groups  subordinate  to  groups — Natural  system — 
Rules  and  difficulties  in  classification,  explained  on  the  theory 
of  descent  with  modification — Classification  of  varieties— De- 
scent always  used  in  classification— Analogical  or  adaptive  char- 
acters—Affinities, general,  complex,  and  radiating— Extinction 
separates  and  defines  groups — MORPHOLOGY,  between  members 
of  the  same  class,  between  parts  of  the  same  individual— EM- 
BRYOLOGY, laws  of,  explained  by  variations  not  supervening 
at  an  early  age,  and  being  inherited  at  a  corresponding  age — 
RUDIMENTARY  ORGANS  :  their  origin  explained — Summary. 

Classification. 

FROM  the  most  remote  period  in  the  history  of  the 
world  organic  beings  have  been  found  to  resemble  each 
other  in  descending  degrees,  so  that  they  can  be  classed 
in  groups  under  groups.  This  classification  is  not  arbi- 
trary like  the  grouping  of  the  stars  in  constellations.  The 
existence  of  groups  would  have  been  of  simple  signifi- 
cance, if  one  group  had  been  exclusively  fitted  to  in- 
habit the  land  and  another  the  water;  one  -to  feed  on 
flesh,  another  on  vegetable  matter,  and  so  on;  but  the 
case  is  widely  different,  for  it  is  notorious  how  com- 
monly members  of  even  the  same  sub-group  have  dif- 
ferent habits.  In  the  second  and  fourth  chapters,  on 
Variation  and  on  Natural  Selection,  I  have  attempted 


CHAP.  XIV.]  CLASSIFICATION.  203 

to  show  that  within  each  country  it  is  the  widely  rang- 
ing, the  much  diffused  and  common,  that  is  the  domi- 
nant species,  belonging  to  the  larger  genera  in  each 
class,  which  vary  most.  The  varieties,  or  incipient  spe- 
cies, thus  produced,  ultimately  become  converted  into 
new  and  distinct  species;  and  these,  on  the  principle 
of  inheritance,  tend  to  produce  other  new  and  domi- 
nant species.  Consequently  the  groups  which  are  now 
large,  and  which  generally  include  many  dominant  spe- 
cies, tend  to  go  on  increasing  in  size.  I  further  at- 
tempted to  show  that  from  the  varying  descendants 
of  each  species  trying  to  occupy  as  many  and  as  differ- 
ent places  as  possible  in  the  economy  of  nature,  they 
constantly  tend  to  diverge  in  character.  This  latter 
conclusion  is  supported  by  observing  the  great  diversity 
of  forms  which,  in  any  small  area,  come  into  the  closest 
competition,  and  by  certain  facts  in  naturalisation. 

I  attempted  also  to  show  that  there  is  a  steady  tend- 
ency in  the  forms  which  are  increasing  in  number 
and  diverging  in  character,  to  supplant  and  exterminate 
the  preceding,  less  divergent  and  less  improved  forms. 
I  request  the  reader  to  turn  to  the  diagram  illustrating 
the  action,  as  formerly  explained,  of  these  several  prin- 
ciples; and  he  will  see  that  the  inevitable  result  is,  that 
the  modified  descendants  proceeding  from  one  progeni- 
tor become  broken  up  into  groups  subordinate  to  groups. 
In  the  diagram  each  letter  on  the  uppermost  line  may 
represent  a  genus  including  several  species,  and  the 
whole  of  the  genera  along  this  upper  line  form  together 
one  class,  for  all  are  descended  from  one  ancient  parent, 
and,  consequently,  have  inherited  something  in  com- 
mon. But  the  three  genera  on  the  left  hand  have, 
on  this  same  principle,  much  in  common,  and  form  a 


204  CLASSIFICATION.  [CHAP.  XIV. 

sub-family,  distinct  from  that  containing  the  next  two 
genera  on  the  right  hand,  which  diverged  from  a  com- 
mon parent  at  the  fifth  stage  of  descent.  These  five 
genera  have  also  much  in  common,  though  less  than 
when  grouped  in  sub-families;  and  they  form  a  family 
distinct  from  that  containing  the  three  genera  still  far- 
ther to  the  right  hand,  which  diverged  at  an  earlier 
period.  And  all  these  genera,  descended  from  (A), 
form  an  order  distinct  from  the  genera  descended  from 
(I).  So  that  we  here  have  many  species  descended  from  a 
single  progenitor  grouped  into  genera;  and  the  genera 
into  sub-families,  families,  and  orders,  all  under  one 
great  class.  The  grand  fact  of  the  natural  subordina- 
tion of  organic  beings  in  groups  under  groups,  which, 
from  its  familiarity,  does  not  always  sufficiently  strike 
us,  is  in  my  judgment  thus  explained.  No  doubt  or- 
ganic beings,  like  all  other  objects,  can  be  classed  in 
many  ways,  either  artificially  by  single  characters,  or 
more  naturally  by  a  number  of  characters.  We  know, 
for  instance,  that  minerals  and  the  elemental  substances 
can  be  thus  arranged.  In  this  case  there  is  of  course  no 
relation  to  genealogical  succession,  and  no  cause  can  at 
present  be  assigned  for  their  falling  into  groups.  But 
with  organic  beings  the  case  is  different,  and  the  view 
above  given  accords  with  their  natural  arrangement  in 
group  under  group;  and  no  other  explanation  has  ever 
been  attempted. 

Naturalists,  as  we  have  seen,  try  to  arrange  the  spe- 
cies, genera,  and  families  in  each  class,  on  what  is  called 
the  Natural  System.  But  what  is  meant  by  this  sys- 
tem? Some  authors  look  at  it  merely  as  a  scheme  for 
arranging  together  those  living  objects  which  are  most 
alike,  and  for  separating  those  which  are  most  unlike; 


CHAP.  XIV.]  CLASSIFICATION.  205 

or  as  an  artificial  method  of  enunciating,  as  briefly  as 
possible,  general  propositions, — that  is,  by  one  sentence 
to  give  the  characters  common,  for  instance,  to  all  mam- 
mals, by  another  those  common  to  all  carnivora,  by 
another  those  common  to  the  dog-genus,  and  then, 
by  adding  a  single  sentence,  a  full  description  is  given 
of  each  kind  of  dog.  The  ingenuity  and  utility  of  this 
system  are  indisputable.  But  many  naturalists  think 
that  something  more  is  meant  by  the  Natural  System; 
they  believe  that  it  reveals  the  plan  of  the  Creator; 
but  unless  it  be  specified  whether  order  in  time  or  space, 
or  both,  or  what  else  is  meant  by  the  plan  of  the  Creator, 
it  seems  to  me  that  nothing  is  thus  added  to  our  knowl- 
edge. Expressions  such  as  that  famous  one  by  Lin- 
naeus, which  we  often  meet  with  in  a  more  or  less  con- 
cealed form,  namely,  that  the  characters  do  not  make 
the  genus,  but  that  the  genus  gives  the  characters,  seem 
to  imply  that  some  deeper  bond  is  included  in  our  classi- 
fications than  mere  resemblance.  I  believe  that  this 
is  the  case,  and  that  community  of  descent — the  one 
known  cause  of  close  similarity  in  organic  beings — is 
the  bond,  which  though  observed  by  various  degrees  of 
modification,  is  partially  revealed  to  us  by  our  classifica- 
tions. * 

Let  us  now  consider  the  rules  followed  in  classifica- 
tion, and  the  difficulties  which  are  encountered  on  the 
view  that  classification  either  gives  some  unknown  plan 
of  creation,  or  is  simply  a  scheme  for  enunciating  gen- 
eral propositions  and  of  placing  together  the  forms  most 
like  each  other.  It  might  have  been  thought  (and 
was  in  ancient  times  thought)  that  those  parts  of  the 
structure  which  determined  the  habits  of  life,  and  the 
general  place  of  each  being  in  the  economy  of  nature, 


206  CLASSIFICATION.  [CHAP.  XIV. 

would  be  of  very  high  importance  in  classification. 
Nothing  can  be  more  false.  No  one  regards  the  ex- 
ternal similarity  of  a  mouse  to  a  shrew,  of  a  dugong  to 
a  whale,  of  a  whale  to  a  fish,  as  of  any  importance. 
These  resemblances,  though  so  intimately  connected 
with  the  whole  life  of  the  being,  are  ranked  as  merely 
"  adaptive  or  analogical  characters; "  but  to  the  con- 
sideration of  these  resemblances  we  shall  recur.  It 
may  even  be  given  as  a  general  rule,  that  the  less  any 
part  of  the  organisation  is  concerned  with  special  habits, 
the  more  important  it  becomes  for  classification.  As 
an  instance:  Owen,  in  speaking  of  the  dugong,  says, 
"  The  generative  organs,  being  those  which  are  most 
remotely  related  to  the  habits  and  food  of  an  animal, 
I  have  always  regarded  as  affording  very  clear  indica- 
tions of  its  true  affinities.  We  are  least  likely  in  the 
modifications  of  these  organs  to  mistake  a  merely  adap- 
tive for  an  essential  character."  With  plants  how- 
remarkable  it  is  that  the  organs  of  vegetation,  on  which 
their  nutrition  and  life  depend,  are  of  little  significa- 
tion; whereas  the  organs  of  reproduction,  with  their  prod- 
uct the  seed  and  embryo,  are  of  paramount  importance! 
So  again  in  formerly  discussing  certain  morphological 
characters  which  are  not  functionally  important,  we 
have  seen  that  they  are  often  of  the  highest  service  in 
classification.  This  depends  on  their  constancy  through- 
out many  allied  groups;  and  their  constancy  chiefly 
depends  on  any  slight  deviations  not  having  been  pre- 
served and  accumulated  by  natural  selection,  which 
acts  only  on  serviceable  characters. 

That  the  mere  physiological  importance  of  an  organ 
does  not  determine  its  classificatory  value,  is  almost 
proved  by  the  fact  that  in  allied  groups,  in  which  the 


CIIAP.  XIV.]  CLASSIFICATION.  207 

same  organ,  as  we  have  every  reason  to  suppose,  has 
nearly  the  same  physiological  value,  its  classificatory 
value  is  widely  different.  No  naturalist  can  have 
worked  long  at  any  group  without  being  struck  with 
this  fact;  and  it  has  been  fully  acknowledged  in  the 
writings  qf  almost  every  author.  It  will  suffice  to  quote 
the  highest  authority,  Robert  Brown,  who,  in  speaking 
of  certain  organs  in  the  Proteaceas,  says  their  generic 
importance,  "  like  that  of  all  their  parts,  not  only  in 
this,  but,  as  I  apprehend,  in  every  natural  family, 
is  very  unequal,  and  in  some  cases  seems  to  be  entirely 
lost."  Again,  in  another  work  he  says,  the  genera 
of  the  Connaraceaj  "  differ  in  having  one  or  more  ovaria, 
in  the  existence  or  absence  of  albumen,  in  the  imbricate 
or  valvular  aestivation.  Any  one  of  these  characters 
singly  is  frequently  of  more  than  generic  importance, 
though  here  even  when  all  taken  together  they  appear 
insufficient  to  separate  Cnestis  from  Connarus."  To 
give  an  example  amongst  insects:  in  one  great  division 
of  the  Hymenoptera,  the  antenna),  as  Westwood  has  re- 
marked, are  most  constant  in  structure;  in  another 
division  they  differ  much,  and  the  differences'  are  of 
quite  subordinate  value  in  classification;  yet  no  one  will 
say  that  the  antenna?  in  these  two  divisions  of  the 
same  order  are  of  unequal  physiological  importance. 
Any  number  of  instances  could  be  given  of  the  varying 
importance  for  classification  of  the  same  important  or- 
gan within  the  same  group  of  beings. 

Again,  no  one  will  say  that  rudimentary  or  atrophied 
organs  are  of  high  physiological  or  vital  importance; 
yet,  undoubtedly,  organs  in  this  condition  are  often  of 
much  value  in  classification.  No  one  will  dispute  that 
the  rudimentary  teeth  in  the  upper  jaws  of  young  rumi- 


208  CLASSIFICATION.  [CHAP.  XIV. 

nants,  and  certain  rudimentary  bones  of  the  leg,  are 
highly  serviceable  in  exhibiting  the  close  affinity  be- 
tween ruminants  and  pachyderms.  Kobert  Brown  has 
strongly  insisted  on  the  fact  that  the  position  of  the 
rudimentary  florets  is  of  the  highest  importance  in  the 
classification  of  the  grasses. 

Numerous  instances  could  be  given  of  characters 
derived  from  parts  which  must  be  considered  of  very 
trifling  physiological  importance,  but  which  are  univer- 
sally admitted  as  highly  serviceable  in  the  definition  of 
whole  groups.  For  instance,  whether  or  not  there  is  an 
open  passage  from  the  nostrils  to  the  mouth,  the  only 
character,  according  to  Owen,  which  absolutely  dis- 
tinguishes fishes  and  reptiles — the  inflection  of  the  angle 
of  the  lower  jaw  in  Marsupials — the  manner  in  which 
the  wings  of  insects  are  folded — mere  colour  in  cer- 
tain Alga3 — mere  pubescence  on  parts  of  the  flower  in 
grasses — the  nature  of  the  dermal  covering,  as  hair  or 
feathers,  in  the  Vertebrata.  If  the  Ornithorhynchus 
had  been  covered  with  feathers  instead  of  hair,  this  ex- 
ternal and  trifling  character  would  have  been  consid- 
ered by  naturalists  as  an  important  aid  in  determin- 
ing the  degree  of  affinity  of  this  strange  creature  to 
birds. 

The  importance,  for  classification,  of  trifling  charac- 
ters, mainly  depends  on  their  being  correlated  with  many 
other  characters  of  more  or  less  importance.  The  value 
indeed  of  an  aggregate  of  characters  is  very  evident  in 
natural  history.  Hence,  as  has  often  been  remarked,  a 
species  may  depart  from  its  allies  in  several  characters, 
both  of  high  physiological  importance,  and  of  almost 
universal  prevalence,  and  yet  leave  us  in  no  doubt  where 
it  should  be  ranked.  Hence,  also,  it  has  been  found 


CIIAP.  XIV.]  CLASSIFICATION.  209 

that  a  classification  founded  on  any  single  character, 
however  important  that  may  be,  has  always  failed;  for 
no  part  of  the  organisation  is  invariably  constant. 
The  importance  of  an  aggregate  of  characters,  even 
when  none  are  important,  alone  explains  the  aphorism 
enunciated  by  Linnaeus,  namely,  that  the  characters  do 
not  give  the  genus,  but  the  genus  gives  the  characters; 
for  this  seems  founded  on  the  appreciation  of  many 
trifling  points  of  resemblance,  too  slight  to  be  denned. 
Certain  plants,  belonging  to  the  Malpighiaceae,  bear 
perfect  and  degraded  flowers;  in  the  latter,  as  A.  de 
Jussieu  has  remarked,  "  the  greater  number  of  the  char- 
acters proper  to  the  species,  to  the  genus,  to  the  family, 
to  the  class,  disappear,  and  thus  laugh  at  our  classifi- 
cation." When  Aspicarpa  produced  in  France,  during 
several  years,  only  these  degraded  flowers,  departing 
so  wonderfully  in  a  number  of  the  most  important 
points  of  structure  from  the  proper  type  of  the  order, 
yet  M.  Richard  sagaciously  saw,  as  Jussieu  observes, 
that  this  genus  should  still  be  retained  amongst  the 
MalpighiaceEe.  This  case  well  illustrates  the  spirit  of 
our  classifications. 

Practically,  when  naturalists  are  at  work,  they  do 
not  trouble  themselves  about  the  physiological  value 
of  the  characters  which  they  use  in  defining  a  group 
or  in  allocating  any  particular  species.  If  they  find 
a  character  nearly  uniform,  and  common  to  a  great 
number  of  forms,  and  not  common  to  others,  they  use 
it  as  one  of  high  value;  if  common  to  some  lesser  num- 
ber, they  use  it  as  of  subordinate  value.  This  principle 
has  been  broadly  confessed  by  some  naturalists  to  be  the 
true  one;  and  by  none  more  clearly  than  by  that  ex- 
cellent botanist,  Aug.  St.  Hilaire.  If  several  trifling 


210  CLASSIFICATION.  [CnAP.  XIV. 

characters  are  always  found  in  combination,  though  no 
apparent  bond  of  connection  can  be  discovered  between 
them,  especial  value  is  set  on  them.  As  in  most  groups 
of  animals,  important  organs,  such  as  those  for  pro- 
pelling the  blood,  or  for  aerating  it,  or  those  for  prop- 
agating the  race,  are  found  nearly  uniform,  they  are 
considered  as  highly  serviceable  in  classification;  but  in 
some  groups  all  these,  the  most  important  vital  organs, 
are  found  to  offer  characters  of  quite  subordinate  value. 
Thus,  as  Fritz  Miiller  has  lately  remarked,  in  the  same 
group  of  crustaceans,  Cypridina  is  furnished  with  a 
heart,  whilst  in  two  closely  allied  genera,  namely  Cypris 
and  Cytherea,  there  is  no  such  organ;  one  species  of 
Cypridina  has  well-developed  branchia?,  whilst  another 
species  is  destitute  of  them. 

We  can  see  why  characters  derived  from  the  embryo 
should  be  of  equal  importance  with  those  derived  from 
the  adult,  for  a  natural  classification  of  course  includes 
all  ages.  But  it  is  by  no  means  obvious,  on  the  ordi- 
nary view,  why  the  structure  of  the  embryo  should  be 
more  important  for  this  purpose  than  that  of  the  adult, 
which  alone  plays  its  full  part  in  the  economy  of  nature. 
Yet  it  has  been  strongly  urged  by  those  great  natural- 
ists, Milne  Edwards  and  Agassiz,  that  embryological 
characters  are  the  most  important  of  all;  and  this  doc- 
trine has  very  generally  been  admitted  as  true.  Never- 
theless, their  importance  has  sometimes  been  exagger- 
ated, owing  to  the  adaptive  characters  of  larva?  not 
having  been  excluded;  in  order  to  show  this,  Fritz 
Miiller  arranged  by  the  aid  of  such  characters  alone  the 
great  class  of  crustaceans,  and  the  arrangement  did  not 
prove  a  natural  one.  But  there  can  be  no  doubt  that 
embryonic,  excluding  larval  characters,  are  of  the  high- 


CHAP.  XIV.]  CLASSIFICATION.  211 

est  value  for  classification,  not  only  with  animals  but 
with  plants.  Thus  the  main  divisions  of  flowering 
plants  are  founded  on  differences  in  the  embryo, — on  the 
number  and  position  of  the  cotyledons,  and  on  the 
mode  of  development  of  the  plumule  and  radicle.  We 
shall  immediately  see  why  these  characters  possess  so 
high  a  value  in  classification,  namely,  from  the  natural 
system  being  genealogical  in  its  arrangement. 

Our  classifications  are  often  plainly  influenced  by 
chains  of  affinities.  Nothing  can  be  easier  than  to  de- 
fine a  number  of  characters  common  to  all  birds;  but 
with  crustaceans,  any  such  definition  has  hitherto  been 
found  impossible.  There  are  crustaceans  at  the  oppo- 
site ends  of  the  series,  which  have  hardly  a  character  in 
common;  yet  the  species  at  both  ends,  from  being  plain- 
ly allied  to  others,  and  these  to  others,  and  so  onwards, 
can  be  recognised  as  unequivocally  belonging  to  this, 
and  to  no  other  class  of  the  Articulata. 

Geographical  distribution  has  often  been  used, 
though  perhaps  not  quite  logically,  in  classification, 
more  especially  in  very  large  groups  of  closely  allied 
forms.  Temminck  insists  on  the  utility  or  even  neces- 
sity of  this  practice  in  certain  groups  of  birds;  and  it 
has  been  followed  by  several  entomologists  and  botanists. 

Finally,  with  respect  to  the  comparative  value  of  the 
various  groups  of  species,  such  as  orders,  sub-orders, 
families,  sub-families,  and  genera,  they  seem  to  be,  at 
least  at  present,  almost  arbitrary.  Several  of  the  best 
botanists,  such  as  Mr.  Bentham  and  others,  have  strong- 
ly insisted  on  their  arbitrary  value.  Instances  could  be 
given  amongst  plants  and  insects,  of  a  group  first  ranked 
by  practised  naturalists  as  only  a  genus,  and  then  raised 
to  the  rank  of  a  sub-family  or  family;  and  this  has 


212  CLASSIFICATION.  [CHAP.  XIV. 

been  done,  not  because  further  research  has  detected 
important  structural  differences,  at  first  overlooked,  but 
because  numerous  allied  species  with  slightly  differ- 
ent grades  of  difference,  have  been  subsequently  dis- 
covered. 

All  the  foregoing  rules  and  aids  and  difficulties  in 
classification  may  be  explained,  if  I  do  not  greatly 
deceive  myself,  on  the  view  that  the  Natural  System  is 
founded  on  descent  with  modification; — that  the  char- 
acters which  naturalists  consider  as  showing  true  affin- 
ity between  any  two  or  more  species,  are  those  which 
have  been  inherited  from  a  common  parent,  all  true 
classification  being  genealogical; — that  community  of 
descent  is  the  hidden  bond  which  naturalists  have  been 
unconsciously  seeking,  and  not  some  unknown  plan  of 
creation,  or  the  enunciation  of  general  propositions, 
and  the  mere  putting  together  and  separating  objects 
more  or  less  alike. 

But  I  must  explain  my  meaning  more  fully.  I  be- 
lieve that  the  arrangement  of  the  groups  within  each 
class,  in  due  subordination  and  relation  to  each  other, 
must  be  strictly  genealogical  in  order  to  be  natural; 
but  that  the  amount  of  difference  in  the  several  branches 
or  .groups,  though  allied  in  the  same  degree  in  blood  to 
their  common  progenitor,  may  differ  greatly,  being  due 
to  the  different  degrees  of  modification  which  they  have 
undergone;  and  this  is  expressed  by  the  forms  being 
ranked  under  different  genera,  families,  sections,  or 
orders.  The  reader  will  best  understand  what  is  meant, 
if  he  will  take  the  trouble  to  refer  to  the  diagram  in  the 
fourth  chapter.  We  will  suppose  the  letters  A  to  L  to 
represent  allied  genera  existing  during  the  Silurian 
epoch,  and  descended  from  some  still  earlier  form.  In 


CHAP.  XIV.]  CLASSIFICATION.  213 

three  of  these  genera  (A,  F,  and  I),  a  species  has  transmit- 
ted modified  descendants  to  the  present  day,  represented 
by  the  fifteen  genera  (a14  to  z14)  on  the  uppermost  hori- 
zontal line.  Now  all  these  modified  descendants  from 
a  single  species,  are  related  in  blood  or  descent  in  the 
same  degree;  they  may  metaphorically  be  called  cousins 
to  the  same  millionth  degree;  yet  they  differ  widely 
and  in  different  degrees  from  each  other.  The  forms 
descended  from  A,  now  broken  up  into  two  or  three 
families,  constitute  a  distinct  order  from  those  de- 
scended from  I,  also  broken  up  into  two  families.  Nor 
can  the  existing  species,  descended  from  A,  be  ranked 
in  the  same  genus  with  the  parent  A;  or  those  from  I, 
with  the  parent  I.  But  the  existing  genus  F14  may  be 
supposed  to  have  been  but  slightly  modified;  and  it 
will  then  rank  with  the  parent-genus  F;  just  as 
some  few  still  living  organisms  belong  to  Silurian 
genera.  So  that  the  comparative  value  of  the  differ- 
ences between  these  organic  beings,  which  are  all  re- 
lated to  each  other  in  the  same  degree  in  blood,  has  come 
to  be  widely  different.  Nevertheless  their  genealogical 
arrangement  remains  strictly  true,  not  only  at  the  pres- 
ent time,  but  at  each  successive  period  of  descent.  All 
the  modified  descendants  from  A  will  have  inherited 
something  in  common  from  their  common  parent,  as 
will  all  the  descendants  from  I;  so  will  it  be  with  each 
subordinate  branch  of  descendants,  at  each  successive 
stage.  If,  however,  we  suppose  any  descendant  of  A, 
or  of  I,  to  have  become  so  much  modified  as  to  have 
lost  all  traces  of  its  parentage,  in  this  case,  its  place  in 
the  natural  system  will  be  lost,  as  seems  to  have  occurred 
with  some  few  existing  organisms.  All  the  descendants 
of  the  genus  F,  along  its  whole  line  of  descent,  are 


214:  CLASSIFICATION.  [CHAP.  XIV. 

supposed  to  have  been  but  little  modified,  and  they  form 
a  single  genus.  But  this  genus,  though  much  isolated, 
will  still  occupy  its  proper  intermediate  position.  The 
representation  of  the  groups,  as  here  given  in  the  dia- 
gram on  a  flat  surface,  is  much  too  simple.  The 
branches  ought  to  have  diverged  in  all  directions.  If 
the  names  of  the  groups  had  been  simply  written  down 
in  a  linear  series,  the  representation  would  have  been 
still  less  natural;  and  it  is  notoriously  not  possible  to 
represent  in  a  series,  on  a  flat  surface,  the  affinities 
which  we  discover  in  nature  amongst  the  beings  of  the 
same  group.  Thus,  the  natural  system  is  genealogical 
in  its  arrangement,  like  a  pedigree:  but  the  amount  of 
modification  which  the  different  groups  have  under- 
gone has  to  be  expressed  by  ranking  them  under  dif- 
ferent so-called  genera,  sub-families,  families,  sections, 
orders,  and  classes. 

It  may  be  worth  while  to  illustrate  this  view  of 
classification,  by  taking  the  case  of  languages.  If  we 
possessed  a  perfect  pedigree  of  mankind,  a  genealogical 
arrangement  of  the  races  of  man  would  afford  the  best 
classification  of  the  various  languages  now  spoken 
throughout  the  world;  and  if  all  extinct  languages,  and 
all  intermediate  and  slowly  changing  dialects,  were  to 
be  included,  such  an  arrangement  would  be  the  only 
possible  one.  Yet  it  might  be  that  some  ancient  lan- 
guages had  altered  very  little  and  had  given  rise  to  few 
new  languages,  whilst  other  had  altered  much  owing  to 
the  spreading,  isolation,  and  state  of  civilisation  of  the 
several  co-descended  races,  and  had  thus  given  rise  to 
many  new  dialects  and  languages.  The  various  degrees 
of  difference  between  the  languages  of  the  same  stock, 
would  have  to  be  expressed  by  groups  subordinate  to 


CHAP.  XIV.]  CLASSIFICATION.  215 

groups;  but  the  proper  or  even  the  only  possible  ar- 
rangement would  still  be  genealogical;  and  this  would 
be  strictly  natural,  as  it  would  connect  together  all  lan- 
guages, extinct  and  recent,  by  the  closest  affinities,  and 
would  give  the  filiation  and  origin  of  each  tongue. 

In  confirmation  of  this  view,  let  us  glance  at  the 
classification  of  varieties,  which  are  known  or  believed 
to  be  descended  from  a  single  species.  These  are 
grouped  under  the  species,  with  the  sub-varieties  under 
the  varieties;  and  in  some  cases,  as  with  the  domestic 
pigeon,  with  several  other  grades  of  difference.  Nearly 
the  same  rules  are  followed  as  in  classifying  species. 
Authors  have  insisted  on  the  necessity  of  arranging 
varieties  on  a  natural  instead  of  an  artificial  system;  we 
are  cautioned,  for  instance,  not  to  class  two  varieties  of 
the  pine-apple  together,  merely  because  their  fruit, 
though  the  most  important  part,  happens  to  be  nearly 
identical;  no  one  puts  the  Swedish  and  common  turnip 
together,  though  the  esculent  and  thickened  stems  are 
so  similar.  Whatever  part  is  found  to  be  most  con- 
stant, is  used  in  classing  varieties:  thus  the  great  agri- 
culturist Marshall  says  the  horns  are  very  useful  for 
this  purpose  with  cattle,  because  they  are  less  variable 
than  the  shape  or  colour  of  the  body,  &c.;  whereas  with 
sheep  the  horns  are  much  less  serviceable,  because  less 
constant.  In  classing  varieties,  I  apprehend  that  if  we 
had  a  real  pedigree,  a  genealogical  classification  would 
be  universally  preferred;  and  it  has  been  attempted  in 
some  cases.  For  we  might  feel  sure,  whether  there  had 
been  more  or  less  modification,  that  the  principle  of 
inheritance  would  keep  the  forms  together  which  were 
allied  in  the  greatest  number  of  points.  In  tumbler 
pigeons,  though  some  of  the  sub-varieties  differ  in  the 


216  -CLASSIFICATION.  [CHAP.  XIV. 

important  character  of  the  length  of  the  beak,  yet  all 
are  kept  together  from  having  the  common  habit  of 
tumbling;  but  the  short-faced  breed  has  nearly  or  quite 
lost  his  habit:  nevertheless,  without  any  thought  on 
the  subject,  these  tumblers  are  kept  in  the  same  group, 
because  allied  in  blood  and  alike  in  some  other  respects. 

With  species  in  a  state  of  nature,  every  naturalist  has 
in  fact  brought  descent  into  his  classification;  for  he 
includes  in  his  lowest  grade,  that  of  species,  the  two 
sexes;  and  how  enormously  these  sometimes  differ  in 
the  most  important  characters,  is  known  to  every  natu- 
ralist: scarcely  a  single  fact  can  be  predicated  in  com- 
mon of  the  adult  males  and  hermaphrodites  of  certain 
cirripedes,  and  yet  no  one  dreams  of  separating  them. 
As  soon  as  the  three  Orchidean  forms,  Monachanthus, 
Myanthus,  and  Catasetum,  which  had  previously  been 
ranked  as  three  distinct  genera,  were  known  to  be  some- 
times produced  on  the  same  plant,  they  were  imme- 
diately considered  as  varieties;  and  now  I  have  been 
able  to  show  that  they  are  the  male,  female,  and  herma- 
phrodite forms  of  the  same  species.  The  naturalist  in- 
cludes as  one  species  the  various  larval  stages  of  the 
same  individual,  however  much  they  may  differ  from 
each  other  and  from  the  adult,  as  well  as  the  so-called 
alternate  generations  of  Steenstrup,  which  can  only  in 
a  technical  sense  be  considered  as  the  same  individual. 
He  includes  monsters  and  varieties,  not  from  their 
partial  resemblance  to  the  parent-form,  but  because 
they  are  descended  from  it. 

As  descent  has  universally  been  used  in  classing  to- 
gether the  individuals  of  the  same  species,  though  the 
males  and  females  and  larvae  are  sometimes  extremely 
different;  and  as  it  has  been  used  in  classing  varieties 


CHAP.  XIV.]  CLASSIFICATION.  217 

which  have  undergone  a  certain,  and  sometimes  a  con- 
siderable amount  of  modification,  may  not  this  same 
element  of  descent  have  been  unconsciously  used  in 
grouping  species  under  genera,  and  genera  under  higher 
groups,  all  under  the  so-called  natural  system?  I  be- 
lieve it  has  been  unconsciously  used;  and  thus  only 
can  I  understand  the  several  rules  and  guides  which 
have  been  followed  by  our  best  systematists.  As  we 
have  no  written  pedigrees,  we  are  forced  to  trace  com- 
munity of  descent  by  resemblances  of  any  kind.  There- 
fore we  chose  those  characters  which  are  the  least  likely 
to  have  been  modified,  in  relation  to  the  conditions 
of  life  to  which  each  species  has  been  recently  exposed. 
Rudimentary  structures  on  this  view  are  as  good  as,  or 
even  sometimes  better  than,  other  parts  of  the  organisa- 
tion. We  care  not  how  trifling  a  character  may  be — let  it 
be  the  mere  inflection  of  the  angle  of  the  jaw,  the  man- 
ner in  which  an  insect's  wing  is  folded,  whether  the 
skin  be  covered  by  hair  or  feathers — if  it  prevail 
throughout  many  and  different  species,  especially  those 
having  very  different  habits  of  life,  it  assumes  high 
value;  for  we  can  account  for  its  presence  in  so  many 
forms  with  such  different  habits,  only  by  inheritance 
from  a  common  parent.  We  may  err  in  this  respect  in 
regard  to  single  points  of  structure,  but  when  several 
characters,  let  them  be  ever  so  trifling,  concur  through- 
out a  large  group  of  beings  having  different  habits,  we 
may  feel  almost  sure,  on  the  theory  of  descent,  that 
these  characters  have  been  inherited  from  a  common 
ancestor;  and  we  know  that  such  aggregated  characters 
have  especial  value  in  classification. 

We  can  understand  why  a  species  or  a  group  of 
species  may  depart  from  its  allies,  in  several  of  its  most 
40 


218  CLASSIFICATION.  [CHAP.  XIV. 

important  characteristics,  and  yet  be  safely  classed  with 
them.  This  may  be  safely  done,  and  is  often  done,  as 
long  as  a  sufficient  number  of  characters,  let  them  be 
ever  so  unimportant,  betrays  the  hidden  bond  of  com- 
munity of  descent.  Let  two  forms  have  not  a  single 
character  in  common,  yet,  if  these  extreme  forms  are 
connected  together  by  a  chain  of  intermediate  groups, 
we  may  at  once  infer  their  community  of  descent,  and 
we  put  them  all  into  the  same  class.  As  we  find  organs 
of  high  physiological  importance — those  which  serve  to 
preserve  life  under  the  most  diverse  conditions  of  exist- 
ence— are  generally  the  most  constant,  we  attach  especial 
value  to  them;  but  if  these  same  organs,  in  another 
group  or  section  of  a  group,  are  found  to  differ  much, 
we  at  once  value  them  less  in  our  classification.  We 
shall  presently  see  why  embryological  characters  are  of 
such  high  classificatory  importance.  Geographical  dis- 
tribution may  sometimes  be  brought  usefully  into  play 
in  classing  large  genera,  because  all  the  species  of  the 
same  genus,  inhabiting  any  distinct  and  isolated  region, 
are  in  all  probability  descended  from  the  same  parents. 

Analogical  Resemblances. — We  can  understand,  on 
the  above  views,  the  very  important  distinction  between 
real  affinities  and  analogical  or  adaptive  resemblances. 
Lamarck  first  called  attention  to  this  subject,  and  he 
has  been  ably  followed  by  Macleay  and  others.  The 
resemblance  in  the  shape  of  the  body  and  in  the  fin-like 
anterior  limbs  between  dugongs  and  whales,  and  be- 
tween these  two  orders  of  mammals  and  fishes,  are  ana- 
logical. So  is  the  resemblance  between  a  mouse  and  a 
shrew-mouse  (Sorex),  which  belong  to  different  orders; 
and  the  still  closer  resemblance,  insisted  on  by  Mr.  Mi- 
vart,  between  the  mouse  and  a  small  marsupial  animal 


CHAP.  XIV.]   ANALOGICAL  RESEMBLANCES.  219 

(Anteehinus)  of  Australia.  These  latter  resemblances 
may  be  accounted  for,  as  it  seems  to  me,  by  adaptation 
for  similarly  active  movements  through  thickets  and 
herbage,  together  with  concealment  from  enemies. 

Amongst  insects  there  are  innumerable  similar  in- 
stances; thus  Ldnna?us,  misled  by  external  appearances, 
actually  classed  an  homopterous  insect  as  a  moth.  We 
see  something  of  the  same  kind  even  with  our  domestic 
varieties,  as  in  the  strikingly  similar  shape  of  the  body 
in  the  improved  breeds  of  the  Chinese  and  common  pig, 
which  are  descended  from  distinct  species;  and  in  the 
similarly  thickened  stems  of  the  common  and  specifically 
distinct  Swedish  turnip.  The  resemblance  between  the 
greyhound  and  the  racehorse  is  hardly  more  fanciful 
than  the  analogies  which  have  been  drawn  by  some 
authors  between  widely  different  animals. 

On  the  view  of  characters  being  of  real  importance 
for  classification,  only  in  so  far  as  they  reveal  descent, 
we  can  clearly  understand  why  analogical  or  adaptive 
characters,  although  of  the  utmost  importance  to  the 
welfare  of  the  being,  are  almost  valueless  to  the  system- 
atist.  For  animals,  belonging  to  two  most  distinct  lines 
of  descent,  may  have  become  adapted  to  similar  condi- 
tions, and  thus  have  assumed  a  close  external  resem- 
blance; but  such  resemblances  will  not  reveal — will 
rather  tend  to  conceal  their  blood-relationship.  "We 
can  thus  also  understand  the  apparent  paradox,  that 
the  very  same  characters  are  analogical  when  one  group 
is  compared  with  another,  but  give  true  affinities  when 
the  members  of  the  same  group  are  compared  together: 
thus,  the  shape  of  the  body  and  fin-like  limbs  are  only 
analogical  when  whales  are  compared  with  fishes, 
being  adaptations  in  both  classes  for  swimming  through 


220  CLASSIFICATION.  [CHAP.  XIV. 

the  water;  but  between  the  several  members  of  the 
whale  family,  the  shape  of  the  body  and  the  fin-like 
limbs  offer  characters  exhibiting  true  affinity;  for  as 
these  parts  are  so  nearly  similar  throughout  the 
whole  family,  we  cannot  doubt  that  they  have 
been  inherited  from  a  common  ancestor.  So  it  is  with 
fishes. 

Numerous  cases  could  be  given  of  striking  resem- 
blances in  quite  distinct  beings  between  single  parts  or 
organs,  which  have  been  adapted  for  the  same  functions. 
A  good  instance  is  afforded  by  the  close  resemblance  of 
the  jaws  of  the  dog  and  Tasmanian  wolf  or  Thylacinus, 
— animals  which  are  widely  sundered  in  the  natural 
system.  But  this  resemblance  is  confined  to  general  ap- 
pearance, as  in  the  prominence  of  the  canines,  and  in  the 
cutting  shape  of  the  molar  teeth.  For  the  teeth  really 
differ  much:  thus  the  dog  has  on  each  side  of  the  upper 
jaw  four  pre-molars  and  only  two  molars;  whilst  the 
Thylacinus  has  three  pre-molars  and  four  molars.  The 
molars  also  differ  much  in  the  two  animals  in  relative 
size  and  structure.  The  adult  dentition  is  preceded  by 
a  widely  different  milk  dentition.  Any  one  may  of 
course  deny  that  the  teeth  in  either  case  have  been 
adapted  for  tearing  flesh,  through  the  natural  selection 
of  successive  variations;  but  if  this  be  admitted  in  the 
one  case,  it  is  unintelligible  to  me  that  it  should  be 
denied  in  the  other.  I  am  glad  to  find  that  so  high  an 
authority  as  Professor  Flower  has  come  to  this  same 
conclusion. 

The  extraordinary  cases  given  in  a  former  chapter, 
of  widely  different  fishes  possessing  electric  organs, — of 
widely  different  insects  possessing  luminous  organs, — 
and  of  orchids  and  asclepiads  having  pollen-masses  with 


CHAP.  XIV.]   ANALOGICAL  RESEMBLANCES.  221 

viscid  discs,  come  under  this  same  head  of  analogical 
resemblances.  But  these  cases  are  so  wonderful  that  they 
were  introduced  as  difficulties  or  objections  to  our 
theory.  In  all  such  cases  some  fundamental  difference 
in  the  growth  or  development  of  the  parts,  and  gen- 
erally in  their  matured  structure,  can  be  detected.  The 
end  gained  is  the  same,  but  the  means,  though  appear- 
ing superficially  to  be  the  same,  are  essentially  different. 
The  principle  formerly  alluded  to  under  the  term  of 
analogical  variation  has  probably  in  these  cases  often 
come  into  play;  that  is,  the  members  of  the  same  class, 
although  only  distantly  allied,  have  inherited  so  much 
in  common  in  their  constitution,  that  they  are  apt  to 
vary  under  similar  exciting  causes  in  a  similar  manner; 
and  this  would  obviously  aid  in  the  acquirement  through 
natural  selection  of  parts  or  organs,  strikingly  like  each 
other,  independently  of  their  direct  inheritance  from  a 
common  progenitor. 

As  species  belonging  to  distinct  classes  have  often, 
been  adapted  by  successive  slight  modifications  to  live 
under  nearly  similar  circumstances, — to  inhabit,  for  in- 
stance, the  three  elements  of  land,  air,  and  water, — we  can 
perhaps  understand  how  it  is  that  a  numerical  paral- 
lelism has  sometimes  been  observed  between  the  sub- 
groups of  distinct  classes.  A  naturalist,  struck  with  a 
parallelism  of  this  nature,  by  arbitrarily  raising  or  sink- 
ing the  value  of  the  groups  in  several  classes  (and  all 
our  experience  shows  that  their  valuation  is  as  yet  arbi- 
trary), could  easily  extend  the  parallelism  over  a  wide 
range;  and  thus  the  septenary,  quinary,  quaternary  and 
ternary  classifications  have  probably  arisen. 

There  is  another  and  curious  class  of  cases  in  which 
close  external  resemblance  does  not  depend  on  adapta- 


222  CLASSIFICATION.  [CnAP.  XIV. 

tion  to  similar  habits  of  life,  but  has  been  gained  for 
the  sake  of  protection.  I  allude  to  the  wonderful  man- 
ner in  which  certain  butterflies  imitate,  as  first  de- 
scribed by  Mr.  Bates,  other  and  quite  distinct  species. 
This  excellent  observer  has  shown  that  in  some  districts 
of  S.  America,  where,  for  instance,  an  Ithomia  abounds 
in  gaudy  swarms,  another  butterfly,  namely,  a  Leptalis, 
is  often  found  mingled  in  the  same  flock;  and  the  latter 
so  closely  resembles  the  Ithomia  in  every  shade  and 
stripe  of  colour  and  even  in  the  shape  of  its  wings,  that 
Mr.  Bates,  with  his  eyes  sharpened  by  collecting  during 
eleven  years,  was,  though  always  on  his  guard,  continu- 
ally deceived.  When  the  mockers  and  the  mocked  are 
caught  and  compared,  they  are  found  to  be  very  differ- 
ent in  essential  structure,  and  to  belong  not  only  to  dis- 
tinct genera,  but  often  to  distinct  families.  Had  this 
mimicry  occurred  in  only  one  or  two  instances,  it  might 
have  been  passed  over  as  a  strange  coincidence.  But,  if 
we  proceed  from  a  district  where  one  Leptalis  imitates 
an  Ithomia,  another  mocking  and  mocked  species  be- 
longing to  the  same  two  genera,  equally  close  in  their 
resemblance,  may  be  found.  Altogether  no  less  than 
ten  genera  are  enumerated,  which  include  species  that 
imitate  other  butterflies.  The  mockers  and  mocked 
always  inhabit  the  same  region;  we  never  find  an  imi- 
tator living  remote  from  the  form  which  it  imitates. 
The  mockers  are  almost  invariably  rare  insects;  the 
mocked  in  almost  every  case  abound  in  swarms.  In 
the  same  district  in  which  a  species  of  Leptalis  closely 
imitates  an  Ithomia,  there  are  sometimes  other  Lepi- 
doptera  mimicking  the  same  Ithomia:  so  that  in  the 
same  place,  species  of  three  genera  of  butterflies  and 
even  a  moth  are  found  all  closely  resembling  a  butter- 


CHAP.  XIV.]   ANALOGICAL  RESEMBLANCES.  223 

fly  belonging  to  a  fourth  genus.  It  deserves  especial 
notice  that  many  of  the  mimicking  forms  of  the  Lep- 
talis,  as  well  as  of  the  mimicked  forms,  can  be  shown 
by  a  graduated  series  to  be  merely  varieties  of  the  same 
species;  whilst  others  are  undoubtedly  distinct  species. 
But  why,  it  may  be  asked,  are  certain  forms  treated 
as  the  mimicked  and  others  as  the  mimickers?  Mr. 
Bates  satisfactorily  answers  this  question,  by  showing 
that  the  form  which  is  imitated  keeps  the  usual  dress 
of  the  group  to  which  it  belongs,  whilst  the  counterfeit- 
ers have  changed  their  dress  and  do  not  resemble  their 
nearest  allies. 

We  are  next  led  to  inquire  what  reason  can  be  as- 
signed for  certain  butterflies  and  moths  so  often  assum- 
ing the  dress  of  another  .and  quite  distinct  form;  why, 
to  the  perplexity  of  naturalists,  has  nature  condescended 
to  the  tricks  of  the  stage?  Mr.  Bates  has,  no  doubt, 
hit  on  the  true  explanation.  The  mocked  forms,  which 
always  abound  in  numbers,  must  habitually  escape  de- 
struction to  a  large  extent,  otherwise  they  could  not 
exist  in  such  swarms;  and  a  large  amount  of  evidence 
has  now  been  collected,  showing  that  they  are  distaste- 
ful to  birds  and  other  insect-devouring  animals.  The 
mocking  forms,  on  the  other  hand,  that  inhabit  the 
same  district,  are  comparatively  rare,  and  belong  to 
rare  groups;  hence  they  must  suffer  habitually  from 
some  danger,  for  otherwise,  from  the  number  of  eggs 
laid  by  all  butterflies,  they  would  in  three  or  four  gen- 
erations swarm  over  the  whole  country.  Now  if  a 
member  of  one  of  these  persecuted  and  rare  groups  were 
to  assume  a  dress  so  like  that  of  a  well-protected  species 
that  it  continually  deceived  the  practised  eyes  of  an 
entomologist,  it  would  often  deceive  predaceous  birds 


224  CLASSIFICATION.  [CHAP.  XIV. 

and  insects,  and  thus  often  escape  destruction.  Mr. 
Bates  may  almost  be  said  to  have  actually  witnessed 
the  process  by  which  the  mimickers  have  come  so  closely 
to  resemble  the  mimicked;  for  he  found  that  some  of 
the  forms  of  Leptalis  which  mimic  so  many  other  butter- 
flies, varied  in  an  extreme  degree.  In  one  district  sev- 
eral varieties  occurred,  and  of  these  one  alone  resembled 
to  a  certain  extent,  the  common  Ithomia  of  the  same 
district.  In  another  district  there  were  two  or  three 
varieties,  one  of  which  was  much  commoner  than  the 
others,  and  this  closely  mocked  another  form  of  Ithomia. 
From  facts  of  this  nature,  Mr.  Bates  concludes  that  the 
Leptalis  first  varies;  and  when  a  variety  happens  to 
resemble  in  some  degree  any  common  butterfly  inhabit- 
ing the  same  district,  this  variety,  from  its  resem- 
blance to  a  flourishing  and  little-persecuted  kind, 
has  a  better  chance  of  escaping  destruction  from 
predaceous  birds  and  insects,  and  is  consequently  oftener 
preserved; — "the  less  perfect  degrees  of  resem- 
blance being  generation  rfter  generation  eliminated, 
and  only  the  others  left  to  propagate  their  kind."  So 
that  here  we  have  an  excellent  illustration  of  natural 
selection. 

Messrs.  Wallace  and  Trimen  have  likewise  described 
several  equally  striking  cases  of  imitation  in  the  Lepi- 
doptera  of  the  Malay  Archipelago  and  Africa,  and  with 
some  other  insects.  Mr.  Wallace  has  also  detected  one 
such  case  with  birds,  but  we  have  none  with  the  larger 
quadrupeds.  The  much  greater  frequency  of  imitation 
with  insects  than  with  other  animals,  is  probably  the 
consequence  of  their  small  size;  insects  cannot  defend 
themselves,  excepting  indeed  the  kinds  furnished  with 
a  string,  and  I  have  never  heard  of  an  instance  of 


CIIAP.  XIV.]   ANALOGICAL  RESEMBLANCES.  225 

such  kinds  mocking  other  insects,  though  they  are 
mocked;  insects  cannot  easily  escape  by  flight  from 
the  larger  animals  which  prey  on  them;  there- 
fore, speaking  metaphorically,  they  are  reduced, 
like  most  weak  creatures,  to  trickery  and  dissimula- 
tion. 

It  should  be  observed  that  the  process  of  imitation 
probably  never  commenced  between  forms  widely  dis- 
similar in  colour.  But  starting  with  species  already 
somewhat  like  each  other,  the  closest  resemblance,  if 
beneficial,  could  readily  be  gained  by  the  above  means; 
and  if  the  imitated  form  was  subsequently  and  gradu- 
ally modified  through  any  agency,  the  imitating  form 
would  be  led  along  the  same  track,  and  thus  be  altered 
to  almost  any  extent,  so  that  it  might  ultimately  assume 
an  appearance  or  colouring  wholly  unlike  that  of  the 
other  members  of  the  family  to  which  it  belonged. 
There  is,  however,  some  difficulty  on  this  head,  for  it 
is  necessary  to  suppose  in  some  cases  that  ancient  mem- 
bers belonging  to  several  distinct  groups,  before  they 
had  diverged  to  their  present  extent,  accidentally  re- 
sembled a  member  of  another  and  protected  group  in 
a  sufficient  degree  to  afford  some  slight  protection;  this 
having  given  the  basis  for  the  subsequent  acquisition  of 
the  most  perfect  resemblance.  - 

On  the  Nature  of  the  Affinities  connecting  Organic 
Beings. — As  the  modified  descendants  of  dominant  spe- 
cies, belonging  to  the  larger  genera,  tend  to  inherit 
the  advantages  which  made  the  groups  to  which  they 
belong  large  and  their  parents  dominant,  they  are  al- 
most sure  to  spread  widely,  and  to  seize  on  more  and 
more  places  in  the  economy  of  nature.  The  larger  and 
more  dominant  groups  within  each  class  thus  tend  to 


226  AFFINITIES  CONNECTING        [CHAP.  XIV. 

go  on  increasing  in  size;  and  they  consequently  sup- 
plant many  smaller  and  feebler  groups.  Thus  we  can 
account  for  the  fact  that  all  organisms,  recent  and  ex- 
tinct, are  included  under  a  few  great  orders,  and  under 
still  fewer  classes.  As  showing  how  few  the  higher 
groups  are  in  number,  and  how  widely  they  are  spread 
throughout  the  world,  the  fact  is  striking  that  the  dis- 
covery of  Australia  has  not  added  an  insect  belonging 
to  a  new  class;  and  that  in  the  vegetable  kingdom,  as 
I  learn  from  Dr.  Hooker,  it  has  added  only  two  or  three 
families  of  small  size. 

In  the  chapter  on  Geological  Succession  I  attempted 
to  show,  on  the  principle  of  each  group  having  generally 
diverged  much  in  character  during  the  long-continued 
process  of  modification,  how  it  is  that  the  more  ancient 
forms  of  life  often  present  characters  in  some  degree 
intermediate  between  existing  groups.  As  some  few  of 
the  old  and  intermediate  forms  have  transmitted  to 
the  present  day  descendants  but  little  modified,  these 
constitute  our  so-called  osculant  or  aberrant  species. 
The  more  aberrant  any  form  is,  the  greater  must  be  the 
number  of  connecting  forms  which  have  been  exter- 
minated and  utterly  lost.  And  we  have  some  evidence 
of  aberrant  groups  having  suffered  severely  from  ex- 
tinction, for  they  are  almost  always  represented  by 
extremely  few  species;  and  such  species  as  do  occur 
are  generally  very  distinct  from  each  other,  which  again 
implies  extinction.  The  genera  Ornithorhynchus  and 
Lepidosiren,  for  example,  would  not  have  been  less  aber- 
rant had  each  been  represented  by  a  dozen  species,  in- 
stead of  as  at  present  by  a  single  one,  or  by  two  or  three. 
We  can,  I  think,  account  for  this  fact  only  by  looking 
at  aberrant  groups  as  forms  which  have  been  con- 


CHAP.  XIV.]  ORGANIC  BEINGS.  227 

quered  by  more  successful  competitors,  with  a  few  mem- 
bers still  preserved  under  unusually  favourable  con- 
ditions. 

Mr.  Waterhouse  has  remarked  that,  when  a  member 
belonging  to  one  group  of  animals  exhibits  an  affinity  to 
a  quite  distinct  group,  this  affinity  in  most  cases  is 
general  and  not  special;  thus,  according  to  Mr.  Water- 
house,  of  all  Rodents,  the  bizcacha  is  most  nearly  related 
to  Marsupials;  but  in  the  points  in  which  it  approaches 
this  order,  its  relations  are  general,  that  is,  not  to  anyone 
marsupial  species  more  than  to  another.  As  these  points 
of  affinity  are  believed  to  be  real  and  not  merely  adap- 
tive, they  must  be  due  in  accordance  with  our  view 
to  inheritance  from  a  common  progenitor.  Therefore 
we  must  suppose  either  that  all  Rodents,  including  the 
bizcacha,  branched  off  from  some  ancient  Marsupial, 
which  will  naturally  have  been  more  or  less  intermediate 
in  character  with  respect  to  all  existing  Marsupials;  or 
that  both  Rodents  and  Marsupials  branched  off  from  a 
common  progenitor,  and  that  both  groups  have  since 
undergone  much  modification  in  divergent  directions. 
On  either  view  we  must  suppose  that  the  bizcacha  has 
retained,  by  inheritance,  more  of  the  characters  of  its 
ancient  progenitor  than  have  other  Rodents;  and  there- 
fore it  will  not  be  specially  related  to  any  one  existing 
Marsupial,  but  indirectly  to  all  or  nearly  all  Marsupials, 
from  having  partially  retained  the  character  of  their 
common  progenitor,  or  of  some  early  member  of  the 
group.  On  the  other  hand,  of  all  Marsupials,  as  Mr. 
Waterhouse  has  remarked,  the  Phascolomys  resembles 
most  nearly,  not  any  one  species,  but  the  general  order 
of  Rodents.  In  this  case,  however,  it  may  be  strongly 
suspected  that  the  resemblance  is  only  analogical,  owing 


228  AFFINITIES  CONNECTING         [CnAr.  XIV. 

to  the  Phascolomys  having  become  adapted  to  habits 
like  those  of  a  Rodent.  The  elder  De  Candolle  has 
made  nearly  similar  observations  on  the  general  nature 
of  the  affinities  of  distinct  families  of  plants. 

On  the  principle  of  the  multiplication  and  gradual 
divergence  in  character  of  the  species  descended  from  a 
common  progenitor,  together  with  their  retention  by 
inheritance  of  some  characters  in  common,  we  can  un- 
derstand the  excessively  complex  and  radiating  affini- 
ties by  which  all  the  members  of  the  same  family  or 
higher  group  are  connected  together.  For  the  common 
progenitor  of  a  whole  family,  now  broken  up  by  ex- 
tinction into  distinct  groups  and  sub-groups,  will  have 
transmitted  some  of  its  characters,  modified  in  various 
ways  and  degrees,  to  all  the  species;  and  they  will  con- 
sequently be  related  to  each  other  by  circuitous  lines 
of  affinity  of  various  lengths  (as  may  be  seen  in  the  dia- 
gram so  often  referred  to),  mounting  up  through  many 
predecessors.  As  it  is  difficult  to  show  the  blood-re- 
lationship between  the  numerous  kindred  of  any  an- 
cient and  noble  family  even  by  the  aid  of  a  genealogical 
tree,  and  almost  impossible  to  do  so  without  this  aid, 
we  can  understand  the  extraordinary  difficulty  which 
naturalists  have  experienced  in  describing,  without  the 
aid  of  a  diagram,  the  various  affinities  which  they  per- 
ceive between  the  many  living  and  extinct  members  of 
the  same  great  natural  class. 

Extinction,  as  we  have  seen  in  the  fourth  chapter, 
has  played  an  important  part  in  defining  and  widening 
the  intervals  between  the  several  groups  in  each  class. 
We  may  thus  account  for  the  distinctness  of  whole  classes 
from  each  other — for  instance,  of  birds  from  all  other 
vertebrate  animals — by  the  belief  that  many  ancient 


CHAP.  XIV.]  ORGANIC  BEINGS.  229 

forms  of  life  have  been  utterly  lost,  through  which  the 
early  progenitors  of  birds  were  formerly  connected  with 
the  early  progenitors  of  the  other  and  at  that  time  less 
differentiated  vertebrate  classes.  There  has  been  much 
less  extinction  of  the  forms  of  life  which  once  connected 
fishes  with  batrachians.  There  has  been  still  less  with- 
in some  whole  classes,  for  instance  the  Crustacea,  for 
here  the  most  wonderfully  diverse  forms  are  still  linked 
together  by  a  long  and  only  partially  broken  chain  of 
affinities.  Extinction  has  only  defined  the  groups:  it 
has  by  no  means  made  them;  for  if  every  form  which 
has  ever  lived  on  this  earth  were  suddenly  to  reappear, 
though  it  would  be  quite  impossible  to  give  definitions 
by  which  each  group  could  be  distinguished,  still  a  natu- 
ral classification,  or  at  least  a  natural  arrangement, 
would  be  possible.  We  shall  see  this  by  turning  to  the 
diagram;  the  letters,  A  to  L,  may  represent  eleven  Si- 
lurian genera,  some  of  which  have  produced  large  groups 
of  modified  descendants,  with  every  link  in  each  branch 
and  sub-branch  still  alive;  and  the  links  not  greater 
than  those  between  existing  varieties.  In  this  case  it 
would  be  quite  impossible  to  give  definitions  by  which 
the  several  members  of  the  several  groups  could  be  dis- 
tinguished from  their  more  immediate  parents  and  de- 
scendants. Yet  the  arrangement  in  the  diagram  would 
still  hold  good  and  would  be  natural;  for,  on  the  prin- 
ciple of  inheritance,  all  the  forms  descended,  for  in- 
stance, from  A,  would  have  something  in  common. 
In  a  tree  we  can  distinguish  this  or  that  branch,  though 
at  the  actual  fork  the  two  unite  and  blend  together. 
We  could  not,  as  I  have  said,  define  the  several  groups; 
but  we  could  pick  out  types,  or  forms,  representing  most 
of  the  characters  of  each  group,  whether  large  or  small, 


230  AFFINITIES  CONNECTING        [CHAP.  XIV. 

and  thus  give  a  general  idea  of  the  value  of  the  differ- 
ences between  them.  This  is  what  we  should  be  driven 
to,  if  we  were  ever  to  succeed  in  collecting  all  the  forms 
in  any  one  class  which  have  lived  throughout  all  time 
and  space.  Assuredly  we  shall  never  succeed  in  mak- 
ing so  perfect  a  collection:  nevertheless,  in  certain 
classes,  we  are  tending  towards  this  end;  and  Milne 
Edwards  has  lately  insisted,  in  an  able  paper,  on  the  high 
importance  of  looking  to  types,  whether  or  not  we  can 
separate  and  define  the  groups  to  which  such  types  be- 
long. 

Finally,  we  have  seen  that  natural  selection,  which 
follows  from  the  struggle  for  existence,  and  which  al- 
most inevitably  leads  to  extinction  and  divergence  of 
character  in  the  descendants  from  anyone  parent-species, 
explains  that  great  and  universal  feature  in  the  affinities 
of  all  organic  beings,  namely,  their  subordination  in 
group  under  group.  "We  use  the  element  of  descent  in 
classing  the  individuals  of  both  sexes  and  of  all  ages 
under  one  species,  although  they  may  have  but  few  char- 
acters in  common;  we  use  descent  in  classing  acknowl- 
edged varieties,  hqwever  different  they  may  be  from 
their  parents;  and  I  believe  that  this  element  of  de- 
scent is  the  hidden  bond  of  connection  which  natur- 
alists have  sought  under  the  term  of  the  Natural  System. 
On  this  idea  of  the  natural  system  being,  in  so  far  as  it 
has  been  perfected,  genealogical  in  its  arrangement,  with 
the  grades  of  difference  expressed  by  the  terms  genera, 
families,  orders.  &c.,  we  can  understand  the  rules  which 
we  are  compelled  to  follow  in  our  classification.  We 
can  understand  why  we  value  certain  resemblances  far 
more  than  others;  why  we  use  rudimentary  and  useless 
organs,  or  others  of  trifling  physiological  importance; 


CHAP.  XIV.]  ORGANIC  BEINGS.  231 

why,  in  finding  the  relations  between  one  group  and 
another,  we  summarily  reject  analogical  or  adaptive 
characters,  and  yet  use  these  same  characters  within 
the  limits  of  the  same  group.  We  can  clearly  see 
how  it  is  that  all  living  and  extinct  forms  can  be 
grouped  together  within  a  few  great  classes;  and  how 
the  several  members  of  each  class  are  connected  to- 
gether by  the  most  complex  and  radiating  lines  of 
affinities.  We  shall  never,  probably,  disentangle  the 
inextricable  web  of  the  affinities  between  the  members 
of  any  one  class;  but  when  we  have  a  distinct  object 
in  view,  and  do  not  look  to  some  unknown  plan  of  crea- 
tion, we  may  hope  to  make  sure  but  slow  pro- 


Professor  Hiickel  in  his  '  Generelle  Morphologic ' 
and  in  other  works,  has  recently  brought  his  great 
knowledge  and  abilities  to  bear  on  what  he  calls  phylo- 
geny,  or  the  lines  of  descent  of  all  organic  beings.  In 
drawing  up  the  several  series  he  trusts  chiefly  to  em- 
bryological  characters,  but  receives  aid  from  homologous 
and  rudimentary  organs,  as  well  as  from  the  successive 
periods  at  which  the  various  forms  of  life  are  believed 
to  have  first  appeared  in  our  geological  formations.  He 
has  thus  boldly  made  a  great  beginning,  and  shows  us 
how  classification  will  in  the  future  be  treated. 

Morphology. 

We  have  seen  that  the  members  of  the  same  class, 
independently  of  their  habits  of  life,  resemble  each  other 
in  the  general  plan  of  their  organisation.  This  resem- 
blance is  often  expressed  by  the  term  "  unity  of  type; " 
or  by  saying  that  the  several  parts  and  organs  in  the 
different  species  of  the  class  are  homologous.  The  whole 


232  MORPHOLOGY.  [CHAP.  XIV. 

subject  is  included  under  the  general  term  of  Morphol- 
ogy. This  is  one  of  the  most  interesting  departments 
of  natural  history,  and  may  almost  be  said  to  be  its  very 
soul.  What  can  be  more  curious  than  that  the  hand 
of  a  man,  formed  for  grasping,  that  of  a  mole  for  dig- 
ging, the  leg  of  the  horse,  the  paddle  of  the  porpoise, 
and  the  wing  of  the  bat,  should  all  be  constructed  on  the 
same  pattern,  and  should  include  similar  bones,  in  the 
same  relative  positions?  How  curious  it  is,  to  give  a 
subordinate  though  striking  instance,  that  the  hind-feet 
of  the  kangaroo,  which  are  so  well  fitted  for  bounding 
over  the  open  plains, — those  of  the  climbing,  leaf-eating 
koala,  equally  well  fitted  for  grasping  the  branches  of 
trees, — those  of  the  ground-dwelling,  insect  or  root  eat- 
ing, bandicoots, — and  those  of  some  other  Australian 
marsupials, — should  all  be  constructed  on  the  same  ex- 
traordinary type,  namely  with  the  bones  of  the  second 
and  third  digits  extremely  slender  and  enveloped  within 
the  same  skin,  so  that  they  appear  like  a  single  toe  fur- 
nished with  two  claws.  Notwithstanding  this  similar- 
ity of  pattern,  it  is  obvious  that  the  hind  feet  of  these 
several  animals  are  used  for  as  widely  different  pur- 
poses as  it  is  possible  to  conceive.  The  case  is  ren- 
dered all  the  more  striking  by  the  American  opossums, 
which  follow  nearly  the  same  habits  of  life  as  some  of 
their  Australian  relatives,  having  feet  constructed  on 
the  ordinary  plan.  Professor  Flower,  from  whom 
these  statements  are  taken,  remarks  in  conclusion:  "We 
may  call  this  conformity  to  type,  without  getting  much 
nearer  to  an  explanation  of  the  phenomenon;"  and 
he  then  adds  "  but  is  it  not  powerfully  suggestive  of 
true  relationship,  of  inheritance  from  a  common  an- 
cestor? " 


CHAP.  XIV.]  MORPHOLOGY.  233 

Geoffrey  St.  Hilaire  has  strongly  insisted  on  the  high 
importance  of  relative  position  or  connexion  in  homo- 
logous parts;  they  may  differ  to  almost  any  extent  in 
form  and  size,  and  yet  remain  connected  together  in  the 
same  invariable  order.  We  never  find,  for  instance,  the 
bones  of  the  arm  and  fore-arm,  or  of  the  thigh  and  leg, 
transposed.  Hence  the  same  names  can  be  given  to  the 
homologous  bones  in  widely  different  animals.  We  see 
the  same  great  law  in  the  construction  of  the  mouths  of 
insects:  what  can  be  more  different  than  the  immensely 
long  spiral  proboscis  of  a  sphinx-moth,  the  curious  folded 
one  of  a  bee  or  bug,  and  the  great  jaws  of  a  beetle? — 
yet  all  these  organs,  serving  for  such  widely  different 
purposes,  are  formed  by  infinitely  numerous  modifica- 
tions of  an  upper  lip,  mandibles,  and  two  pairs  of  max- 
illae. The  same  law  governs  the  construction  of  the 
mouths  and  limbs  of  crustaceans.  So  it  is  with  the 
flowers  of  plants. 

Nothing  can  be  more  hopeless  than  to  attempt  to 
explain  this  similarity  of  pattern  in  members  of  the 
same  class,  by  utility  or  by  the  doctrine  of  final  causes. 
The  hopelessness  of  the  attempt  has  been  expressly  ad- 
mitted by  Owen  in  his  most  interesting  work  on  the 
'  Nature  of  Limbs.'  On  the  ordinary  view  of  the  in- 
dependent creation  of  each  being,  we  can  only  say  that 
so  it  is; — that  it  has  pleased  the  Creator  to  construct 
all  the  animals  and  plants  in  each  great  class  on  a  uni- 
form plan;  but  this  is  not  a  scientific  explanation. 

The  explanation  is  to  a  large  extent  simple  on  the 
theory  of  the  selection  of  successive  slight  modifications, 
— each  modification  being  profitable  in  some  way  to  the 
modified  form,  but  often  affecting  by  correlation  other 
parts  of  the  organisation.  In  changes  of  this  nature, 
41 


234  MORPHOLOGY.  [CHAP.  XIV. 

there  will  be  little  or  no  tendency  to  alter  the  original 
pattern,  or  to  transpose  the  parts.  The  bones  of  a  limb 
might  be  shortened  and  flattened  to  any  extent,  becom- 
ing at  the  same  time  enveloped  in  thick  membrane,  so 
as  to  serve  as  a  fin;  or  a  webbed  hand  might  have  all 
its  bones,  or  certain  bones,  lengthened  to  any  extent, 
with  the  membrane  connecting  them  increased,  so  as 
to  serve  as  a  wing;  yet  all  these  modifications  would 
not  tend  to  alter  the  framework  of  the  bones  or  the  rela- 
tive connection  of  the  parts.  If  we  suppose  that  an 
early  progenitor — the  archetype  as  it  may  be  called — 
of  all  mammals,  birds,  and  reptiles,  had  its  limbs  con- 
structed on  the  existing  general  pattern,  for  whatever 
purpose  they  served,  we  can  at  once  perceive  the  plain 
signification  of  the  homologous  construction  of  the  limbs 
throughout  the  class.  So  with  the  mouths  of  insects, 
we  have  only  to  suppose  that  their  common  progenitor 
had  an  upper  lip,  mandibles,  and  two  pairs  of  maxillce, 
these  parts  being  perhaps  very  simple  in  form;  and 
then  natural  selection  will  account  for  the  infinite  di- 
versity in  the  structure  and  functions  of  the  mouths 
of  insects.  Nevertheless,  it  is  conceivable  that  the  gen- 
eral pattern  of  an  organ  might  become  so  much  obscured 
as  to  be  finally  lost,  by  the  reduction  and  ultimately 
by  the  complete  abortion  of  certain  parts,  by  the 
fusion  of  other  parts,  and  by  the  doubling  or  multi- 
plication of  others, — variations  which  we  know  to  be 
within  the  limits  of  possibility.  In  the  paddles  of  the 
gigantic  extinct  sea-lizards,  and  in  the  mouths 
of  certain  suctorial  crustaceans,  the  general  pattern 
seems  thus  to  have  become  partially  obscured. 

There  is  another  and  equally  curious  branch  of  our 
subject;  namely,  serial  homologies,  or  the  comparison 


CHAP.  XIV.]  MORPHOLOGY.  235 

of  the  different  parts  or  organs  in  the  same  individual, 
and  not  of  the  same  parts  or  organs  in  different  mem- 
bers of  the  same  class.  Most  physiologists  believe  that 
the  bones  of  the  skull  are  homologous — that  is,  cor- 
respond in  number  and  in  relative  connexion — with 
the  elemental  parts  of  a  certain  number  of  vertebra?. 
The  anterior  and  posterior  limbs  in  all  the  higher  verte- 
brate classes  are  plainly  homologous.  So  it  is  with 
the  wonderfully  complex  jaws  and  legs  of  crustaceans. 
It  is  familiar  to  almost  every  one,  that  in  a  flower  the 
relative  position  of  the  sepals,  petals,  Stamens,  and  pis- 
tils, as  well  as  their  intimate  structure,  are  intelligible 
on  the  view  that  they  consist  of  metamorphosed  leaves, 
arranged  in  a  spire.  In  monstrous  plants,  we  often  get 
direct  evidence  of  the  possibility  of  one  organ  being 
transformed  into  another;  and  we  can  actually  see,  dur- 
ing the  early  or  embryonic  stages  of  development  in 
flowers,  as  well  as  in  crustaceans  and  many  other  ani- 
mals, that  organs,  which  when  mature  become  extremely 
different  are  at  first  exactly  alike. 

How  inexplicable  are  the  cases  of  serial  homologies 
on  the  ordinary  view  of  creation!  Why  should  the 
brain  be  enclosed  in  a  box  composed  of  such  numerous 
and  such  extraordinarily  shaped  pieces  of  bone,  appa- 
rently representing  vertebrae?  As  Owen  has  remarked, 
the  benefit  derived  from  the  yielding  of  the  separate 
pieces  in  the  act  of  parturition  by  mammals,  will  by 
no  means  explain  the  same  construction  in  the  skulls 
of  birds  and  reptiles.  Why  should  similar  bones  have 
been  created  to  form  the  wing  and  the  leg  of  a  bat,  used 
as  they  are  for  such  totally  different  purposes,  namely 
flying  and  walking?  Why  should  one  crustacean,  which 
has  an  extremely  complex  mouth  formed  of  many  parts, 


23G  MORPHOLOGY.  [CHAP.  XIV. 

consequently  always  have  fewer  legs;  or  conversely,  those 
with  many  legs  have  simpler  mouths?  Why  should 
the  sepals,  petals,  stamens,  and  pistils,  in  each  flower, 
though  fitted  for  such  distinct  purposes,  be  all  con- 
structed on  the  same  pattern? 

On  the  theory  of  natural  selection,  we  can,  to  a  cer- 
tain extent,  answer  these  questions.  We  need  not  here 
consider  how  the  bodies  of  some  animals  first  became 
divided  into  a  series  of  segments,  or  how  they  became 
divided  into  right  and  left  sides,  with  corresponding 
organs,  for  such  questions  are  almost  beyond  investiga- 
tion. It  is,  however,  probable  that  some  serial  struc- 
tures are  the  result  of  cells  multiplying  by  division, 
entailing  the  multiplication  of  the  parts  developed  from 
such  cells.  It  must  suffice  for  our  purpose  to  bear  in 
mind  that  an  indefinite  repetition  of  the  same  part  or 
organ  is  the  common  characteristic,  as  Owen  has  re- 
marked, of  all  low  or  little  specialised  forms;  therefore 
the  unknown  progenitor  of  the  Vertebrata  probably  pos- 
sessed many  vertebrae;  the  unknown  progenitor  of  the 
Articulata,  many  segments;  and  the  unknown  progeni- 
tor of  flowering  plants,  many  leaves  arranged  in  one 
or  more  spires.  We  have  also  formerly  seen  that  parts 
many  times  repeated  are  eminently  liable  to  vary,  not 
only  in  number,  but  in  form.  Consequently  such  parts, 
being  already  present  in  considerable  numbers,  and 
being  highly  variable,  would  naturally  afford  the  ma- 
terials for  adaptation  to  the  most  different  purposes; 
yet  they  would  generally  retain,  through  the  force  of 
inheritance,  plain  traces  of  their  original  or  fundamental 
resemblance.  They  would  retain  this  resemblance  all 
the  more,  as  the  variations,  which  afforded  the  basis  for 
their  subsequent  modification  through  natural  selection, 


CHAP.  XIV.]  MORPHOLOGY.  237 

would  tend  from  the  first  to  be  similar;  the  parts  be- 
ing at  an  early  stage  of  growth  alike,  and  being  sub- 
jected to  nearly  the  same  conditions.  Such  parts, 
whether  more  or  less  modified,  unless  their  common 
origin  became  wholly  obscured,  would  be  serially  homo- 
logous. 

In  the  great  class  of  molluscs,  though  the  parts  in 
distinct  species  can  be  shown  to  be  homologous,  only  a 
few  serial  homologies,  such  as  the  valves  of  Chitons, 
can  be  indicated;  that  is,  we  are  seldom  enabled  to  say 
that  one  part  is  homologous  with  another  part  in  the 
same  individual.  And  we  can  understand  this  fact; 
for  in  molluscs,  even  in  the  lowest  members  of  the  class, 
we  do  not  find  nearly  so  much  indefinite  repetition  of 
any  one  part  as  we  find  in  the  other  great  classes  of  the 
animal  and  vegetable  kingdoms. 

But  morphology  is  a  much  more  complex  subject 
than  it  at  first  appears,  as  has  lately  been  well  shown 
in  a  remarkable  paper  by  Mr.  E.  Ray  Lankester,  who 
has  drawn  an  important  distinction  between  certain 
classes  of  cases  which  have  all  been  equally  ranked  by 
naturalists  as  homologous.  He  proposes  to  call  the 
structures  which  resemble  each  other  in  distinct  ani- 
mals, owing  to  their  descent  from  a  common  progenitor 
with  subsequent  modification,  homogenous;  and  the  re- 
semblances which  cannot  thus  be  accounted  for,  he  pro- 
poses to  call  homoplastic.  For  instance,  he  believes  that 
the  hearts  of  birds  and  mammals  are  as  a  whole  homo- 
genous,— that  is,  have  been  derived  from  a  common  pro- 
genitor; but  that  the  four  cavities  of  the  heart  in  the 
two  classes  are  homoplastic, — that  is,  have  been  inde- 
pendently developed.  Mr.  Lankester  also  adduces  the 
close  resemblance  of  the  parts  on  the  right  and  left  sides 


238  MORPHOLOGY.  [Cnxp.  XIV. 

of  the  body,  and  in  the  successive  segments  of  the  same 
individual  animal;  and  here  we  have  parts  commonly 
called  homologous,  which  bear  no  relation  to  the  descent 
of  distinct  species  from  a  common  progenitor.  Homo- 
plastic  structures  are  the  same  with  those  which  I  have 
classed,  though  in  a  very  imperfect  manner,  as  analo- 
gous modifications  or  resemblances.  Their  formation 
may  be  attributed  in  part  to  distinct  organisms,  or  to 
distinct  parts  of  the  same  organism,  having  varied  in  an 
analogous  manner;  and  in  part  to  similar  modifica- 
tions, having  been  preserved  for  the  same  general  pur- 
pose or  function, — of  which  many  instances  have  been 
given. 

Naturalists  frequently  speak  of  the  skull  as  formed 
of  metamorphosed  vertebrae;  the  jaws  of  crabs  as  meta- 
morphosed legs;  the  stamens  and  pistils  in  flowers  as 
metamorposed  leaves;  but  it  would  in  most  cases  be 
more  correct,  as  Professor  Huxley  has  remarked,  to  speak 
of  both  skull  and  vertebra,  jaws  and  legs,  &c.,  as  hav- 
ing been  metamorphosed,  not  one  from  the  other,  as  they 
now  exist,  but  from  some  common  and  simpler  element. 
Most  naturalists,  however,  use  such  language  only  in 
a  metaphorical  sense;  they  are  far  from  meaning  that 
during  a  long  course  of  descent,  primordial  organs  of  any 
kind — vertebrae  in  the  one  case  and  legs  in  the  other — 
have  actually  been  converted  into  skulls  or  jaws.  Yet 
so  strong  is  the  appearance  of  this  having  occurred,  that 
naturalists  can  hardly  avoid  employing  language 
having  this  plain  signification.  According  to  the  views 
here  maintained,  such  language  may  be  used  literally; 
and  the  wonderful  fact  of  the  jaws,  for  instance,  of  a 
crab  retaining  numerous  characters  which  they  probably 
would  have  retained  through  inheritance,  if  they  had 


CHAP.  XIV].  DEVELOPMENT  AND  EMBRYOLOGY.        239 

really  been  metamorphosed  from  true  through  extremely 
simple  legs,  is  in  part  explained. 


Development  and  Embryology. 

This  is  one  of  the  most  important  subjects  in  the 
whole  round  of  history.  The  metamorphoses  of  insects, 
with  which  every  one  is  familiar,  are  generally  effected 
abruptly  by  a  few  stages;  but  the  transformations  are 
in  reality  numerous  and  gradual,  though  concealed. 
A  certain  ephemerous  insect  (Chloeon)  during  its  devel- 
opment, moults,  as  shown  by  Sir  J.  Lubbock,  above 
twenty  times,  and  each  time  undergoes  a  certain  amount 
of  change;  and  in  this  case  we  see  the  act  of  metamor- 
phosis performed  in  a  primary  and  gradual  manner. 
Many  insects,  and  especially  certain  crustaceans,  show 
us  what  wonderful  changes  of  structure  can  be  effected 
during  development.  Such  changes,  however,  reach 
their  acme  in  the  so-called  alternate  generations  of 
some  of  the  lower  animals.  It  is,  for  instance,  an  as- 
tonishing fact  that  a  delicate  branching  coralline,  stud- 
ded with  polypi  and  attached  to  a  submarine  rock, 
should  produce,  first  by  budding  and  then  by  transverse 
division,  a  host  of  huge  floating  jelly-fishes;  and  that 
these  should  produce  eggs,  from  which  are  hatched  swim- 
ming animalcules,  which  attach  themselves  to  rocks 
and  become  developed  into  branching  corallines;  and  so 
on  in  an  endless  cycle.  The  belief  in  the  essential  iden- 
tity of  the  process  of  alternate  generation  and  of  ordi- 
nary metamorphosis  has  been  greatly  strengthened  by 
Wagner's  discovery  of  the  larva  or  maggot  of  a  fly,  name- 
ly the  Cecidomyia,  producing  asexually  other  larvae, 
and  these  others,  which  finally  are  developed  into  ma- 


24:0        DEVELOPMENT  AND  EMBRYOLOGY.  [CHAP.  XIV. 

ture  males  and  females,  propagating  their  kind  in  the 
ordinary  manner  by  eggs. 

It  may  be  worth  notice  that  when  Wagner's  remark- 
able discovery  was  first  announced,  I  was  asked  how 
was  it  possible  to  account  for  the  larva?  of  this  fly  hav- 
ing acquired  the  power  of  asexual  reproduction.  As 
long  as  the  case  remained  unique  no  answer  could  be 
given.  But  already  Grimm  has  shown  that  another  fly, 
a  Chironomus,  reproduces  itself  in  nearly  the  same  man- 
ner, and  he  believes  that  this  occurs  frequently  in  the 
Order.  It  is  the  pupa,  and  not  the  larva,  of  the  Chiro- 
nomus which  has  this  power;  and  Grimm  further  shows 
that  this  case,  to  a  certain  extent,  "  unites  that  of  the 
Cecidomyia  with  the  parthenogenesis  of  the  Coccidae; " 
— the  term  parthenogenesis  implying  that  the  mature 
females  of  the  Coccida?  are  capable  of  producing  fertile 
eggs  without  the  concourse  of  the  males.  Certain  ani- 
mals belonging  to  several  classes  are  now  known  to  have 
the  power  of  ordinary  reproduction  at  an  unusually 
early  age;  and  we  have  only  to  accelerate  parthenoge- 
netic  production  by  gradual  steps  to  an  earlier  and  ear- 
lier age, — Chironomus  showing  us  an  almost  exactly  in- 
termediate stage,  viz.,  that  of  the  pupa — and  we  can 
perhaps  account  for  the  marvellous  case  of  the  Cecido- 
myia. 

It  has  already  been  stated  that  various  parts  in  the 
same  individual  which  are  exactly  alike  during  an  early 
embryonic  period,  become  widely  different  and  serve 
for  widely  different  purposes  in  the  adult  state.  So 
again  it  has  been  shown  that  generally  the  embryos  of 
the  most  distinct  species  belonging  to  the  same  class 
are  closely  similar,  but  become,  when  fully  developed, 
widely  dissimilar.  A  better  proof  of  this  latter  fact 


CHAP.  XIV.]  DEVELOPMENT  AND  EMBRYOLOGY.        241 

cannot  be  given  than  the  statement  by  Von  Baer  that 
"the  embryos  of  mammalia,  of  birds,  lizards,  and 
"  snakes,  probably  also  of  chelonia  are  in  their  earliest 
"  states  exceedingly  like  one  another,  both  as  a  whole 
"  and  in  the  mode  of  development  of  their  parts;  so 
"  much  so,  in  fact,  that  we  can  often  distinguish  the 
"  embryos  only  by  their  size.  In  my  possession  are  two 
"  little  embryos  in  spirit,  whose  names  I  have  omitted 
"  to  attach,  and  at  present  I  am  quite  unable  to  say  to 
"  what  class  they  belong.  They  may  be  lizards  or  small 
"birds,  or  very  young  mammalia,  so  complete  is 
"  the  similarity  in  the  mode  of  formation  of  the  head 
"  and  trunk  in  these  animals.  The  extremities,  how- 
"ever,  are  still  absent  in  these  embryos.  But  even 
"  if  they  had  existed  in  the  earliest  stage  of  their  de- 
"  velopment  we  should  learn  nothing,  for  the  feet  of 
"  lizards  and  mammals,  the  wings  and  feet  of  birds, 
"  no  less  than  the  hands  and  feet  of  man,  all  arise  from 
"  the*  same  fundamental  form."  The  larvae  of  most 
crustaceans,,  at  corresponding  stages  of  development, 
closely  resemble  each  other,  however  different  the  adults 
may  become;  and  so  it  is  with  very  many  other  ani- 
mals. A  trace  of  the  law  of  embryonic  resemblance 
occasionally  lasts  till  a  rather  late  age:  thus  birds  of 
the  same  genus,  and  of  allied  genera,  often  resemble 
each  other  in  their  immature  plumage;  as  we  see  in  the 
spotted  feathers  in  the  young  of  the  thrush  group.  In 
the  cat  tribe,  most  of  the  species  when  adult  are  striped 
or  spotted  in  lines;  and  stripes  or  spots  can  be  plainly 
distinguished  in  the  whelp  of  the  lion  and  the  puma. 
We  occasionally  though  rarely  see  something  of  the 
same  kind  in  plants;  thus  the  first  leaves  of  the  ulex  or 
furze,  and  the  first  leaves  of  the  phyllodineous  acacias, 


242      DEVELOPMENT  AND  EMBRYOLOGY.  [CHAP.  XIV. 

are  pinnate  or  divided  like  the  ordinary  leaves  of  the 
leguminosae. 

The  points  of  structure,  in  which  the  embryos  of 
widely  different  animals  within  the  same  class  resemble 
each  other,  often  have  no  direct  relation  to  their  con- 
ditions of  existence.  We  cannot,  for  instance,  sup- 
pose that  in  the  embryos  of  the  vertebrata  the  peculiar 
loop-like  courses  of  the  arteries  near  the  branchial  slits 
are  related  to  similar  conditions, — in  the  young  mam- 
mal which  is  nourished  in  the  womb  of  its  mother,  in 
the  egg  of  the  bird  which  is  hatched  in  a  nest,  and  in 
the  spawn  of  a  frog  under  water.  We  have  no  more 
reason  to  believe  in  such  a  relation,  than  we  have  to  be- 
lieve that  the  similar  bones  in  the  hand  of  a  man,  wing 
of  a  bat,  and  fin  of  a  porpoise,  are  related  to  similar  con- 
ditions of  life.  No  one  supposes  that  the  stripes  on  the 
whelp  of  a  lion,  or  the  spots  on  the  young  blackbird, 
are  of  any  use  to  these  animals. 

The  case,  however,  is  different  when  an  animal  dur- 
ing any  part  of  its  embryonic  career  is  active,  and  has  to 
provide  for  itself.  The  period  of  activity  may  come  on 
earlier  or  later  in  life;  but  whenever  it  comes  on,  the 
adaptation  of  the  larva  to  its  conditions  of  life  is  just  as 
perfect  and  as  beautiful  as  in  the  adult  animal.  In  how 
important  a  manner  this  has  acted,  has  recently  been 
well  shown  by  Sir  J.  Lubbock  in  his  remarks  on  the 
close  similarity  of  the  Iarva3  of  some  insects  belonging  to 
very  different  orders,  and  on  the  dissimilarity  of  the 
larvas  of  other  insects  within  the  same  order,  according 
to  their  habits  of  life.  Owing  to  such  adaptations,  the 
similarity  of  the  larva  of  allied  animals  is  sometimes 
greatly  obscured;  especially  when  there  is  a  division  of 
labour  during  the  different  stages  of  development,  as 


CHAP.  XIV.]  DEVELOPMENT  AND  EMBRYOLOGY.        343 

when  the  same  larva  has  during  one  stage  to  search  for 
food,  and  during  another  stage  has  to  search  for  a  place 
of  attachment.  Cases  can  even  be  given  of  the  larvae  of 
allied  species,  or  groups  of  species,  differing  more  from 
each  other  than  do  the  adults.  In  most  cases,  however, 
the  larvae,  though  active,  still  obey,  more  or  less  closely, 
the  law  of  common  embryonic  resemblance.  Cirripedes 
afford  a  good  instance  of  this;  even  the  illustrious  Cu- 
vier  did  not  perceive  that  a  barnacle  was  a  crustacean: 
but  a  glance  at  the  larva  shows  this  in  an  unmistakable 
manner.  So  again  the  two  main  divisions  of  cirripedes, 
the  pedunculated  and  sessile,  though  differing  widely  in 
external  appearance,  have  larvae  in  all  their  stages  barely 
distinguishable. 

The  embryo  in  the  course  of  development  generally 
rises  in  organisation;  I  use  this  expression,  though  I  am 
aware  that  it  is  hardly  possible  to  define  clearly  what  is 
meant  by  the  organisation  being  higher  or  lower.  But 
no  one  probably  will  dispute  that  the  butterfly  is  higher 
than  the  caterpillar.  In  some  cases,  however,  the  ma- 
ture animal  must  be  considered  as  lower  in  the  scale 
than  the  larva,  as  with  certain  parasitic  crustaceans. 
To  refer  once  again  to  cirripedes:  the  larvae  in  the  first 
stage  have  three  pairs  of  locomotive  organs,  a  simple 
single  eye,  and  a  probosciformed  mouth,  with  which 
they  feed  largely,  for  they  increase  much  in  size.  In 
the  second  stage,  answering  to  the  chrysalis  stage  of 
butterflies,  they  have  six  pairs  of  beautifully  constructed 
natatory  legs,  a  pair  of  magnificent  compound  eyes,  and 
extremely  complex  antennas;  but  they  have  a  closed 
and  imperfect  mouth,  and  cannot  feed:  their  function  at 
this  stage  is,  to  search  out  by  their  well-developed  or- 
gans of  sense,  and  to  reach  by  their  active  powers  of 


244       DEVELOPMENT  AND  EMBRYOLOGY.  [CHAP.  XIV. 

swimming,  a  proper  place  on  which  to  become  attached 
and  to  undergo  their  final  metamorphosis.  When  this 
is  completed  they  are  fixed  for  life:  their  legs  are  now 
converted  into  prehensile  organs;  they  again  obtain  a 
well-constructed  mouth;  but  they  have  no  antennaa,  and 
their  two  eyes  are  now  reconverted  into  a  minute,  single, 
simple  eye-spot.  In  this  last  and  complete  state,  cirri- 
pedes  may  be  considered  as  either  more  highly  or  more 
lowly  organised  than  they  were  in  the  larval  condition. 
But  in  some  genera  the  larvae  become  developed  into 
hermaphrodites  having  the  ordinary  structure,  and  into 
what  I  have  called  complemental  males;  and  in  the 
latter  the  development  has  assuredly  been  retrograde, 
for  the  male  is  a  mere  sack,  which  lives  for  a  short  time 
and  is  destitute  of  mouth,  stomach,  and  every  other 
organ  of  importance,  excepting  those  for  reproduction. 

We  are  so -much  accustomed  to  see  a  difference  in 
structure  between  the  embryo  and  the  adult,  that  we  are 
tempted  to  look  at  this  difference  as  in  some  necessary 
manner  contingent  on  growth.  But  there  is  no  reason 
why,  for  instance,  the  wing  of  a  bat,  or  the  fin  of  a  por- 
poise, should  not  have  been  sketched  out  with  all  their 
parts  in  proper  proportion,  as  soon  as  any  part  became 
visible.  In  some  whole  groups  of  animals  and  in  cer- 
tain members  of  other  groups  this  is  the  case,  and  the 
embryo  does  not  at  any  period  differ  widely  from  the 
adult:  thus  Owen  has  remarked  in  regard  to  cuttle-fish, 
"  there  is  no  metamorphosis;  the  cephalopodic  char- 
acter is  manifested  long  before  the  parts  of  the  embryo 
are  completed."  Land-shells  and  fresh-water  crusta- 
ceans are  born  having  their  proper  forms,  whilst  the 
marine  members  of  the  same  two  great  classes  pass 
through  considerable  and  often  great  changes  during 


CHAP.  XIV.]      DEVELOPMENT  AND  EMBRYOLOGY.  245 

their  development.  Spiders,  again,  barely  undergo  any. 
metamorphosis.  The  larvae  of  most  insects  pass  through 
a  worm-like  stage,  whether  they  are  active  and  adapted 
to  diversified  habits,  or  are  inactive  from  being  placed 
in  the  midst  of  proper  nutriment  or  from  being  fed  by 
their  parents;  but  in  some  few  cases,  as  in  that  of  Aphis, 
if  we  look  to  the  admirable  drawings  of  the  develop- 
ment of  this  insect,  by  Professor  Huxley,  we  see  hardly 
any  trace  of  the  vermiform  stage. 

Sometimes  it  is  only  the  earlier  developmental  stages 
which  fail.  Thus  Fritz  Miiller  has  made  the  remark- 
able discovery  that  certain  shrimp-like  crustaceans  (al- 
lied to  Penceus)  first  appear  under  the  simple  nauplius- 
f orm,  and  after  passing  through  two  or  more  zoea-stages, 
and  then  through  the  mysis-stage,  finally  acquire  their 
mature  structure:  now  in  the  whole  great  malacostracan 
order,  to  which  these  crustaceans  belong,  no  other  mem- 
ber is  as  yet  known  to  be  first  developed  under  the  nau- 
plius-form,  though  many  appear  as  zoeas;  nevertheless 
Miiller  assigns  reasons  for  his  belief,  that  if  there  had 
been  no  suppression  of  development,  all  these  crusta- 
ceans would  have  appeared  as  nauplii. 

How,  then,  can  we  explain  these  several  facts  in 
embryology ,— namely,  the  very  general,  though  not  uni- 
versal, difference  in  structure  between  the  embryo  and 
the  adult; — the  various  parts  in  the  same  individual 
embryo,  which  ultimately  become  very  unlike  and  serve 
for  diverse  purposes,  being  at  an  early  period  of  growth 
alike; — the  common,  but  not  invariable,  resemblance 
between  the  embryos  or  larvae  of  the  most  distinct  spe- 
cies in  the  same  class; — the  embryo  often  retaining 
whilst  within  the  egg  or  womb,  structures  which  are 
of  no  service  to  it,  either  at  that  or  at  a  later  period  of 


24G       DEVELOPMENT  AND  EMBRYOLOGY.  [CIIAP.  XIV. 

life;  on  the  other  hand  larvae,  which  have  to  provide 
for  their  own  wants,  being  perfectly  adapted  to  the  sur- 
rounding conditions; — and  lastly  the  fact  of  certain 
larvae  standing  higher  in  the  scale  of  organisation  than 
the  mature  animal  into  which  they  are  developed?  I 
believe  that  all  these  facts  can  be  explained,  as  follows. 

It  is  commonly  assumed,  perhaps  from  monstrosities 
affecting  the  embryo  at  a  very  early  period,  that  slight 
variations  or  individual  differences  necessarily  appear 
at  an  equally  early  period.  We  have  little  evidence  on 
this  head,  but  what  we  have  certainly  points  the  other 
way;  for  it  is  notorious  that  breeders  of  cattle,  horses, 
and  various  fancy  animals,  cannot  positively  tell,  until 
some  time  after  birth,  what  will  be  the  merits  or  de- 
merits of  their  young  animals.  We  see  this  plainly  in 
our  own  children;  we  cannot  tell  whether  a  child  will 
be  tall  or  short,  or  what  its  precise  features  will  be. 
The  question  is  not,  at  what  period  of  life  each  variation 
may  have  been  caused,  but  at  what  period  the  effects 
are  displayed.  The  cause  may  have  acted,  and  I  believe 
often  has  acted,  on  one  or  both  parents  before  the  act  of 
generation.  It  deserves  notice  that  it  is  of  no  import- 
ance to  a  very  young  animal,  as  long  as  it  remains  in 
its  mother's  womb  or  in  the  egg,  or  as  Jong  as  it  is 
nourished  and  protected  by  its  parent,  whether  most  of 
its  characters  are  acquired  a  little  earlier  or  later  in  life. 
It  would  not  signify,  for  instance,  to  a  bird  which  ob- 
tained its  food  by  having  a  much-curved  beak  whether 
or  not  whilst  young  it  possessed  a  beak  of  this  shape, 
as  long  as  it  was  fed  by  its  parents. 

I  have  stated  in  the  first  chapter,  that  at  whatever 
age  a  variation  first  appears  in  the  parent,  it  tends  to 
re-appear  at  a  corresponding  age  in  the  offspring.  Ce> 


CHAP.  XIV.]  DEVELOPMENT  AND  EMBRYOLOGY.      247 

tain  variations  can  only  appear  at  corresponding  ages; 
for  instance,  peculiarities  in  the  caterpillar,  cocoon, 
or  imago  states  of  the  silk-moth:  or,  again,  in  the  full- 
grown  horns  of  cattle.  But  variations,  which,  for  all 
that  we  can  see  might  have  first  appeared  either  earlier 
or  later  in  life,  likewise  tend  to  reappear  at  a  corre- 
sponding age  in  the  offspring  and  parent.  I  am 
far  from  meaning  that  this  is  invariably  the  case,  and 
I  could  give  several  exceptional  cases  of  variations 
(taking  the  word  in  the  largest  sense)  which  have  su- 
pervened at  an  earlier  age  in  the  child  than  in  the 
parent. 

These  two  principles,  namely,  that  slight  variations 
generally  appear  at  a  not  very  early  period  of  life,  and 
are  inherited  at  a  corresponding  not  early  period,  ex- 
plain, as  I  believe,  all  the  above  specified  leading  facts 
in  embryology.  But  first  let  us  look  to  a  few  analo- 
gous cases  in  our  domestic  varieties.  Some  authors 
who  have  written  on  Dogs,  maintain  that  the  greyhound 
and  bulldog,  though  so  different,  are  really  closely  al- 
lied varieties,  descended  from  the  same  wild  stock;  hence 
I  was  curious  to  see  how  far  their  puppies  differed  from 
each  other:  I  was  told  by  breeders  that  they  differed 
just  as  much  as  their  parents,  and  this,  judging  by  the 
eye,  seemed  almost  to  be  the  case;  but  on  actually  meas- 
uring the  old  dogs  and  their  six-days-old  puppies,  I 
found  that  the  puppies  had  not  acquired  nearly  their 
full  amount  of  proportional  difference.  So,  again,  I 
was  told  that  the  foals  of  cart  and  race-horses — breeds 
which  have  been  almost  wholly  formed  by  selection 
under  domestication — differed  as  much  as  the  full-grown 
animals;  but  having  had  careful  measurements  made 
of  the  dams  and  of  three-days-old  colts  of  race  and 


248      DEVELOPMENT  AND  EMBRYOLOGY.  [CHAP.  XIV. 

heavy  cart-horses,  I  find  that  this  is  by  no  means  the 
case. 

As  we  have  conclusive  evidence  that  the  breeds  of 
the  Pigeon  are  descended  from  a  single  wild  species,  I 
compared  the  young  within  twelve  hours  after  being 
hatched;  I  carefully  measured  the  proportions  (but  will 
not  here  give  the  details)  of  the  beak,  width  of  mouth, 
length  of  nostril  and  of  eyelid,  size  of  feet  and  length 
of  leg,  in  the  wild  parent-species,  in  pouters,  fantails, 
runts,  barbs,  dragons,  carriers,  and  tumblers.  Now 
some  of  these  birds,  when  mature,  differ  in  so  extraordi- 
nary a  manner  in  the  length  and  form  of  beak,  and  in 
other  characters,  that  they  would  certainly  have  been 
ranked  as  distinct  genera  if  found  in  a  state  of  nature. 
But  when  the  nestling  birds  of  these  several  breeds  were 
placed  in  a  row,  though  most  of  them  could  just  be  dis- 
tinguished, the  proportional  differences  in  the  above 
specified  points  were  incomparably  less  than  in  the  full- 
grown  birds.  Some  characteristic  points  of  difference 
— for  instance,  that  of  the  width  of  mouth — could  hardly 
be  detected  in  the  young.  But  there  was  one  remark- 
able exception  to  this  rule,  for  the  young  of  the  short- 
faced  tumbler  differed  from  the  young  of  the  wild  rock- 
pigeon  and  of  the  other  breeds,  in  almost  exactly  the 
same  proportions  as  in  the  adult  state. 

These  facts  are  explained  by  the  above  two  principles. 
Fanciers  select  their  dogs,  horses,  pigeons,  &c.,  for  breed- 
ing, when  nearly  grown  up:  they  are  indifferent  whether 
the  desired  qualities  are  acqiiired  earlier  or  later  in 
life,  if  the  full-grown  animal  possesses  them.  And 
the  cases  just  given,  more  especially  that  of  the  pigeons, 
show  that  the  characteristic  differences  which  have  been 
accumulated  by  man's  selection,  and  which  give  value  to 


CHAP.  XIV.]  DEVELOPMENT  AND  EMBRYOLOGY.       249 

his  breeds,  do  not  generally  appear  at  a  very  early  period 
of  life,  and  are  inherited  at  a  corresponding  not  early 
period.  But  the  case  of  the  short-faced  tumbler,  which 
when  twelve  hours  old  possessed  its  proper  characters, 
proves  that  this  is  not  the  universal  rule;  for  here  the 
characteristic  differences  must  either  have  appeared  at 
an  earlier  period  than  usual,  or,  if  not  so,  the  differences 
must  have  been  inherited,  not  at  a  corresponding,  but  at 
an  earlier  age. 

Now  let  us  apply  these  two  principles  to  species  in  a 
state  of  nature.  Let  us  take  a  group  of  birds,  descended 
from  some  ancient  form  and  modified  through  natural 
selection  for  different  habits.  Then,  from  the  many 
slight  successive  variations  having  supervened  in  the 
several  species  at  a  not  early  age,  and  having  been  in- 
icrited  at  a  corresponding  age,  the  young  will  have  been 
but  little  modified,  and  they  will  still  resemble  each 
other  much  more  closely  than  do  the  adults, — just  as  we 
have  seen  with  the  breeds  of  the  pigeon.  We  may  ex- 
tend this  view  to  widely  distinct  structures  and  to  whole 
classes.  The  fore-limbs,  for  instance,  which  once  served 
as  legs  to  a  remote  progenitor,  may  have  become,  through 
a  long  course  of  modification,  adapted  in  one  descendant 
to  act  as  hands,  in  another  as  paddles,  in  another  as 
wings;  but  on  the  above  two  principles  the  fore-limbs 
will  not  have  been  much  modified  in  the  embryos  of 
these  several  forms;  although  in  each  form  the  fore- 
limb  will  differ  greatly  in  the  adult  state.  Whatever 
influence  long-continued  use  or  disuse  may  have  had  in 
modifying  the  limbs  or  other  parts  of  any  species,  this 
will  chiefly  or  solely  have  affected  it  when  nearly  ma- 
ture, when  it  was  compelled  to  use  its  full  powers  to 
gain  its  own  living;  and  the  effects  thus  produced  will 
42 


250      DEVELOPMENT  AND  EMBRYOLOGY.  [CHAP.  XIV. 

have  been  transmitted  to  the  offspring  at  a  correspond- 
ing nearly  mature  age.  Thus  the  young  will  not  be 
modified,  or  will  be  modified  only  in  a  slight  degree, 
through  the  effects  of  the  increased  use  or  disuse  of 
parts. 

With  some  animals  the  successive  variations  may 
have  supervened  at  a  very  early  period  of  life,  or  the 
steps  may  have  been  inherited  at  an  earlier  age  than 
that  at  which  they  first  occurred.  In  either  of  these 
cases,  the  young  or  embryo  will  closely  resemble  the  ma- 
ture parent-form,  as  we  have  seen  with  the  short-faced 
tumbler.  And  this  is  the  rule  of  development  in  certain 
whole  groups,  or  in  certain  sub-groups  alone,  as  with 
cuttle-fish,  land-shells,  fresh-water  crustaceans,  spiders, 
and  some  members  of  the  great  class  of  insects.  With 
respect  to  the  final  cause  of  the  young  in  such  groups 
not  passing  through  any  metamorphosis,  we  can  see 
that  this  would  follow  from  the  following  contingencies; 
namely,  from  the  young  having  to  provide  at  a  very 
early  age  for  their  own  wants,  and  from  their  following 
the  same  habits  of  life  with  their  parents;  for  in  this 
case,  it  would  be  indispensable  for  their  existence  that 
they  should  be  modified  in  the  same  manner  as  their 
parents.  Again,  with  respect  to  the  singular  fact  that 
many  terrestrial  and  fresh-water  animals  do  not  under- 
go any  metamorphosis,  whilst  marine  members  of  the 
same  groups  pass  through  various  transformations,  Fritz 
Miiller  has  suggested  that  the  process  of  slowly  modify- 
ing and  adapting  an  animal  to  live  on  the  land  or  in 
fresh  water,  instead  of  in  the  sea,  would  be  greatly  sim- 
plified by  its  not  passing  through  any  larval  stage;  for  it 
is  not  probable  that  places  well  adapted  for  both  the 
larval  and  mature  stages,  under  such  new  and  greatly 


CHAP.  XIV.]  DEVELOPMENT  AND  EMBRYOLOGY.       251 

changed  habits  of  life,  would  commonly  be  found  unoc- 
cupied or  ill-occupied  by  other  organisms.  In  this  case 
the  gradual  acquirement  at  an  earlier  and  earlier  age 
of  the  adult  structure  would  be  favoured  by  natural  selec- 
tion; and  all  traces  of  former  metamorphoses  would 
finally  be  lost. 

If,  on  the  other  hand,  it  profited  the  young  of  an 
animal  to  follow  habits  of  life  slightly  different  from 
those  of  the  parent-form,  and  consequently  to  be  con- 
structed on  a  slightly  different  plan,  or  if  it  profited  a 
larva  already  different  from  its  parent  to  change  still 
further,  then,  on  the  principle  of  inheritance  at  corre- 
sponding ages,  the  young  or  the  Iarva3  might  be  ren- 
dered by  natural  selection  more  and  more  different  from 
their  parents  to  any  conceivable  extent.  Differences  in 
the  larva  might,  also,  become  correlated  with  successive 
stages  of  its  development;  so  that  the  larva,  in  the  first 
stage,  might  come  to  differ  greatly  from  the  larva  in  the 
second  stage,  as  is  the  case  with  many  animals.  The 
adult  might  also  become  fitted  for  sites  or  habits,  in 
which  organs  of  locomotion  or  of  the  senses,  &c.,  would 
be  useless;  and  in  this  case  the  metamorphosis  would 
be  retrograde. 

From  the  remarks  just  made  we  can  see  how  by 
changes  of  structure  in  the  young,  in  conformity  with 
changed  habits  of  life,  together  with  inheritance  at  cor- 
responding ages,  animals  might  come  to  pass  through 
stages  of  development,  perfectly  distinct  from  the  pri- 
mordial condition  of  their  adult  progenitors.  Most  of 
our  best  authorities  are  now  convinced  that  the  various 
larval  and  pupal  stages  of  insects  have  thus  been  acquired 
through  adaptation,  and  not  through  inheritance  from 
some  ancient  form.  The  curious  case  of  Sitaris — a 


'252      DEVELOPMENT  AND  EMBRYOLOGY.  [CHAP.  XIV. 

beetle  which  passes  through  certain  unusual  stages  of 
development — will  illustrate  how  this  might  occur.  The 
first  larval  form  is  described  by  M.  Fabre,  as  an  active, 
minute  insect,  furnished  with  six  legs,  two  long  anten- 
nas, and  four  eyes.  These  larva?  are  hatched  in  the 
nests  of  bees;  and  when  the  male-bees  emerge  from 
their  burrows,  in  the  spring,  which  they  do  before  the 
females,  the  larva?  spring  on  them,  and  afterwards  crawl 
on  to  the  females  whilst  paired  with  the  males.  As 
soon  as  the  female  bee  deposits  her  eggs  on  the  surface 
of  the  honey  stored  in  the  cells,  the  larvae  of  the  Sitaris 
leap  on  the  eggs  and  devour  them.  Afterwards  they 
undergo  a  complete  change;  their  eyes  disappear;  their 
legs  and  antennae  become  rudimentary,  and  they  feed  on 
honey;  so  that  they  now  more  closely  resemble  the  ordi- 
nary larvae  of  insects;  ultimately  they  undergo  a  further 
transformation,  and  finally  emerge  as  the  perfect  beetle. 
Now,  if  an  insect,  undergoing  transformations  like  those 
of  the  Sitaris,  were  to  become  the  progenitor  of  a  whole 
new  class  of  insects,  the  course  of  development  of  the 
new  class  would  be  widely  different  from  that  of  our 
existing  insects;  and  the  first  larval  stage  certainly 
would  not  represent  the  former  condition  of  any  adult 
and  ancient  form. 

On  the  other  hand  it  is  highly  probable  that  with 
many  animals  the  embryonic  or  larval  stages  show  us, 
more  or  less  completely,  the  condition  of  the  progenitor 
of  the  whole  group  in  its  adult  state.  In  the  great  class 
of  the  Crustacea,  forms  wonderfully  distinct  from  each 
other,  namely,  suctorial  parasites,  cirripedes,  entomo- 
straca,  and  even  the  malacostraca,  appear  at  first  as 
larvae  under  the  nauplius-form;  and  as  these  larvae  live 
and  feed  in  the  open  sea,  and  are  not  adapted  for  any 


CHAP.  XIV.]  DEVELOPMENT  AND  EMBRYOLOGY.      253 

peculiar  habits  of  life,  and  from  other  reasons  assigned 
by  Fritz  Mtiller,  it  is  probable  that  at  some  very  remote 
period  an  independent  adult  animal,  resembling  the 
Nauplius,  existed,  and  subsequently  produced,  along  sev- 
eral divergent  lines  of  descent,  the  above-named  great 
Crustacean  groups.  So  again  it  is  probable,  from  what 
we  know  of  the  embryos  of  mammals,  birds,  fishes,  and 
reptiles,  that  these  animals  are  the  modified  descen- 
dants of  some  ancient  progenitor,  which  was  furnished 
in  its  adult  state  with  branchiae,  a  swim-bladder,  four 
fin-like  limbs,  and  a  long  tail,  all  fitted  for  an  aquatic 
life. 

As  all  the  organic  beings,  extinct  and  recent,  which 
have  ever  lived,  can  be  arranged  within  a  few  great 
classes;  and  as  all  within  each  class  have,  according  to 
our  theory,  been  connected  together  by  fine  gradations, 
the  best,  and,  if  our  collections  were  nearly  perfect,  the 
only  possible  arrangement,  would  be  genealogical;  de- 
ecent  being  the  hidden  bond  of  connexion  which  natural- 
ists have  been  seeking  under  the  term  of  the  Natural 
System.  On  this  view  we  can  understand  how  it  is  that, 
in  the  eyes  of  most  naturalists,  the  structure  of  the  em- 
bryo is  even  more  important  for  classification  than  that 
of  the  adult.  In  two  or  more  groups  of  animals,  how- 
ever much  they  may  differ  from  each  other  in  structure 
and  habits  in  their  adult  condition,  if  they  pass  through 
closely  similar  embryonic  stages,  we  may  feel  assured 
that  they  all  are  descended  from  one  parent-form,  and 
are  therefore  closely  related.  Thus,  community  in  em- 
bryonic structure  reveals  community  of  descent;  but 
dissimilarity  in  embryonic  development  does  not  prove 
discommunity  of  descent,  for  in  one  of  two  groups  the 
developmental  stages  may  have  been  suppressed,  or  may 


254      DEVELOPMENT  AND  EMBRYOLOGY.  [CHAP.  XIV. 

have  been  so  greatly  modified  through  adaptation  to 
new  habits  of  life,  as  to  be  no  longer  recognisable.  Even 
in  groups,  in  which  the  adults  have  been  modified  to 
an  extreme  degree,  community  of  origin  is  often  re- 
vealed by  the  structure  of  the  larvae;  we  have  seen,  for 
instance,  that  cirripedes,  though  externally  so  like  shell- 
fish, are  at  once  known  by  their  larva?  to  belong  to  the 
great  class  of  crustaceans.  As  the  embryo  often  shows 
us  more  or  less  plainly  the  structure  of  the  less  modi- 
fied and  ancient  progenitor  of  the  group,  we  can  see 
why  ancient  and  extinct  forms  so  often  resemble  in  their 
adult  state  the  embryos  of  existing  species  of  the  same 
class.  Agassiz  believes  this  to  be  a  universal  law  of 
nature;  and  we  may  hope  hereafter  to  see  the  law  proved 
true.  It  can,  however,  be  proved  true  only  in  those 
cases  in  which  the  ancient  state  of  the  progenitor  of 
the  group  has  not  been  wholly  obliterated,  either  by 
successive  variations  having  supervened  at  a  very  early 
period  of  growth,  or  by  such  variations  having  been  in- 
herited at  an  earlier  age  than  that  at  which  they  first 
appeared.  It  should  also  be  borne  in  mind,  that  the 
law  may  be  true,  but  yet,  owing  to  the  geological  record 
not  extending  far  enough  back  in  time,  may  remain  for 
a  long  period,  or  for  ever,  incapable  of  demonstration. 
The  law  will  not  strictly  hold  good  in  those  cases  in 
which  an  ancient  form  became  adapted  in  its  larval  state 
to  some  special  line  of  life,  and  transmitted  the  same 
larval  state  to  a  whole  group  of  descendants;  for  such 
larva?  will  not  resemble  any  still  more  ancient  form  in 
its  adult  state. 

Thus,  as  it  seems  to  me,  the  leading  facts  in  embry- 
ology, which  are  second  to  none  in  importance,  are  ex- 
plained on  the  principle  of  variations  in  the  many  de- 


CHAP.  XIV.]         RUDIMENTARY  ORGANS.  255 

scendants  from  some  one  ancient  progenitor,  having  ap- 
peared at  a  not  very  early  period  of  life,  and  having  been 
inherited  at  a  corresponding  period.  Embryology  rises 
greatly  in  interest,  when  we  look  at  the  embryo  as  a 
picture,  more  or  less  obscured,  of  the  progenitor,  either 
in  its  adult  or  larval  state,  of  all  the  members  of  the 
same  great  class. 

Rudimentary,  Atrophied,  and  Aborted  Organs. 

Organs  or  parts  in  this  strange  condition,  bearing  the 
plain  stamp  of  inutility,  are  extremely  common,  or  even 
general,  throughout  nature.  It  would  be  impossible  to 
name  one  of  the  higher  animals  in  which  some  part  or 
other  is  not  in  a  rudimentary  condition.  In  the  mam- 
malia, for  instance,  the  males  possess  rudimentary  mam- 
mae; in  snakes  one  lobe  of  the  lungs  is  rudimentary; 
in  birds  the  "  bastard-wing  "  may  safely  be  considered 
as  a  rudimentary  digit,  and  in  some  species  the  whole 
wing  is  so  far  rudimentary  that  it  cannot  be  used  for 
flight.  What  can  be  more  curious  than  the  presence 
of  teeth  in  fcetal  whales,  which  when  grown  up  have 
not  a  tooth  in  their  heads;  or  the  teeth,  which  never 
cut  through  the  gums,  in  the  upper  jaws  of  unborn 
calves? 

Eudimentary  organs  plainly  declare  their  origin  and 
meaning  in  various  ways.  There  are  beetles  belonging 
to  closely  allied  species,  or  even  to  the  same  identical 
species,  which  have  either  full-sized  and  perfect  wings, 
or  mere  rudiments  of  membrane,  which  not  rarely  lie 
under  wing-covers  firmly  soldered  together;  and  in  these 
cases  it  is  impossible  to  doubt,  that  the  rudiments  repre- 
sent wings.  Eudimentary  organs  sometimes  retain  their 
potentiality:  this  occasionally  occurs  with  the  mam- 


256  RUDIMENTARY,   ATROPHIED.     [CHAP.  XIV. 

mas  of  male  mammals,  which  have  been  known  to  be- 
come well  developed  and  to  secrete  milk.  So  again  in 
the  udders  in  the  genus  Bos,  there  are  normally  four 
developed  and  two  rudimentary  teats;  but  the  latter  in 
our  domestic  cows  sometimes  become  well  developed 
and  yield  milk.  In  regard  to  plants  the  petals  are  some- 
times rudimentary,  and  sometimes  well-developed  in  the 
individuals  of  the  same  species.  In  certain  plants  hav- 
ing separated  sexes  Kolreuter  found  that  by  crossing 
a  species,  in  which  the  male  flowers  included  a  rudiment 
of  a  pistil,  with  an  hermaphrodite  species,  having  of 
course  a  well-developed  pistil,  the  rudiment  in  the  hy- 
brid offspring  was  much  increased  in  size;  and  this  clear- 
ly shows  that  the  rudimentary  and  perfect  pistils  are  es- 
sentially alike  in  nature.  An  animal  may  possess  various 
parts  in  a  perfect  state,  and  yet  they  may  in  one  sense 
be  rudimentary,  for  they  are  useless:  thus  the  tadpole 
of  the  common  Salamander  or  Water-newt,  as  Mr.  G.  H. 
Lewes  remarks,  "has  gills,  and  passes  its  existence  in 
"  the  water;  but  the  Salamandra  atra,  which  lives  high 
"  up  among  the  mountains,  brings  forth  its  young  f ull- 
"  formed.  This  animal  never  lives  in  the  water.  Yet 
"  if  we  open  a  gravid  female,  we  find  tadpoles  inside  her 
"with  exquisitely  feathered  gills;  and  when  placed  in 
"  water  they  swim  about  like  the  tadpoles  of  the 
"  water-newt.  Obviously  this  aquatic  organisation  has 
"no  reference  to  the  future  life  of  the  animal,  nor 
"  has  it  any  adaptation  to  its  embryonic  condition;  it 
"  has  solely  reference  to  ancestral  adaptations,  it 
"repeats  a  phase  in  the  development  of  its  progeni- 
"  tors." 

An  organ,  serving  for  two  purposes,  may  become 
rudimentary  or  utterly  aborted  for  one,  even  the  more 


CHAP.  XIV.]         AND  ABORTED  ORGANS.  257 

important  purpose,  and  remain  perfectly  efficient  for 
the  other.  Thus  in  plants,  the  office  of  the  pistil  is  to 
allow  the  pollen-tubes  to  reach  the  ovules  within  the 
ovarium.  The  pistil  consists  of  a  stigma  supported  on 
a  style;  but  in  some  Composite,  the  male  florets,  which 
of  course  cannot  be  fecundated,  have  a  rudimentary 
pistil,  for  it  is  not  crowned  with  a  stigma;  but  the  style 
remains  well  developed  and  is  clothed  in  the  usual  man- 
ner with  hairs,  which  serve  to  brush  the  pollen  out  of 
the  surrounding  and  conjoined  anthers.  Again,  an  or- 
gan may  become  rudimentary  for  its  proper  purpose, 
and  be  used  for  a  distinct  one:  in  certain  fishes  the 
swim-bladder  seems  to  be  rudimentary  for  its  proper 
function  of  giving  buoyancy,  but  has  become  converted 
into  a  nascent  breathing  organ  or  lung.  Many  similar 
instances  could  be  given. 

Useful  organs,  however  little  they  may  be  developed, 
unless  we  have  reason  to  suppose  that  they  were  for- 
merly more  highly  developed,  ought  not  to  be  consid- 
ered as  rudimentary.  Th2y  may  be  in  a  nascent  condi- 
tion, and  in  progress  towards  further  development. 
Rudimentary  organs,  on  the  other  hand,  are  either  quite 
useless,  such  as  teeth  which  never  cut  through  the  gums, 
or  almost  useless,  such  as  the  wings  of  an  ostrich,  which 
serve  merely  as  sails.  As  organs  in  this  condition  would 
formerly,  when  still  less  developed,  have  been  of  even 
less  use  than  at  present,  they  cannot  formerly  have  been 
produced  through  variation  and  natural  selection,  which 
acts  solely  by  the  preservation  of  useful  modifications. 
They  have  been  partially  retained  by  the  power  of  in- 
heritance, and  relate  to  a  former  state  of  things.  It  is, 
however,  often  difficult  to  distinguish  between  rudimen- 
tary and  nascent  organs;  for  we  can  judge  only  by  analogy 


258  RUDIMENTARY,   ATROPHIED,     [CHAP.  XIV. 

whether  a  part  is  capable  of  further  development,  in 
which  case  alone  it  deserves  to  be  called  nascent.  Or- 
gans in  this  condition  will  always  be  somewhat  rare; 
for  beings  thus  provided  will  commonly  have  been  sup- 
planted by  their  successors  with  the  same  organ  in  a 
more  perfect  state,  and  consequently  will  have  become 
long  ago  extinct.  The  wing  of  the  penguin  is  of  high 
service,  acting  as  a  fin;  it  may,  therefore,  represent  the 
nascent  state  of  the  wing:  not  that  I  believe  this  to  be 
the  case;  it  is  more  probably  a  reduced  organ,  modi- 
fied for  a  new  function:  the  wing  of  the  Apteryx,  on  the 
other  hand,  is  quite  useless,  and  is  truly  rudimentary. 
Owen  considers  the  simple  filamentary  limbs  of  the  Lepi- 
dosiren  as  the  "  beginnings  of  organs  which  attain  full 
functional  development  in  higher  vertebrates; "  but,  ac- 
cording to  the  view  lately  advocated  by  Dr.  Giinther, 
they  are  probably  remnants,  consisting  of  the  persist- 
ent axis  of  a  fin,  with  the  lateral  rays  or  branches  abort- 
ed. The  mammary  glands  of  the  Ornithorhynchus  may 
be  considered,  in  comparison  with  the  udders  of  a  cow, 
as  in  a  nascent  condition.  The  ovigerous  frena  of  cer- 
tain cirripedes,  which  have  ceased  to  give  attachment 
to  the  ova  and  are  feebly  developed,  are  nascent  bran- 
chiae. 

Rudimentary  organs  in  the  individuals  of  the  same 
species  are  very  liable  to  vary  in  the  degree  of  their 
development  and  in  other  respects.  In  closely  allied 
species,  also,  the  extent  to  which  the  same  organ  has 
been  reduced  occasionally  differs  much.  This  latter  fact 
is  well  exemplified  in  the  state  of  the  wings  of  female 
moths  belonging  to  the  same  family.  Rudimentary  or- 
gans may  be  utterly  aborted;  and  this  implies,  that  in 
certain  animals  or  plants,  parts  are  entirely  absent  which 


CHAP.  XIV.]         AND  ABORTED  ORGANS.  259 

analogy  would  lead  us  to  expect  to  find  in  them,  and 
which  are  occasionally  found  in  monstrous  individuals. 
Thus  in  most  of  the  Scrophulariaceae  the  fifth  stamen 
is  utterly  aborted;  yet  we  may  conclude  that  a  fifth 
stamen  once  existed,  for  a  rudiment  of  it  is  found  in 
many  species  of  the  family,  and  this  rudiment  occasion- 
ally becomes  perfectly  developed,  as  may  sometimes 
be  seen  in  the  common  snap-dragon.  In  tracing  the 
homologies  of  any  part  in  different  members  of  the  same 
class,  nothing  is  more  common,  or,  in  order  fully  to  un- 
derstand the  relations  of  the  parts,  more  useful  than 
the  discovery  of  rudiments.  This  is  well  shown  in  the 
drawings  given  by  Owen  of  the  leg-bones  of  the  horse, 
ox,  and  rhinoceros. 

It  is  an  important  fact  that  rudimentary  organs,  such 
as  teeth  in  the  upper  jaws  of  whales  and  ruminants,  can 
often  be  detected  in  the  embryo,  but  afterwards  wholly 
disappear.  It  is  also,  I  believe,  a  universal  rule,  that 
a  rudimentary  part  is  of  greater  size  in  the  embryo  rela- 
tively to  the  adjoining  parts,  than  in  the  adult;  so  that 
the  organ  at  this  early  age  is  less  rudimentary,  or  even 
cannot  be  said  to  be  in  any  degree  rudimentary.  Hence 
rudimentary  organs  in  the  adult  are  often  said  to  have 
retained  their  embryonic  condition. 

I  have  now  given  the  leading  facts  with  respect  to 
rudimentary  organs.  In  reflecting  on  them,  every  one 
must  be  struck  with  astonishment;  for  the  same  reason- 
ing power  which  tells  us  that  most  parts  and  organs  are 
exquisitely  adapted  for  certain  purposes,  tells  us  with 
equal  plainness  that  these  rudimentary  or  atrophied 
organs  are  imperfect  and  useless.  In  works  on  natural 
history,  rudimentary  organs  are  generally  said  to  have 
been  created  "  for  the  sake  of  symmetry,"  or  in  order 


2GO  RUDIMENTARY,   ATROPHIED,     [CHAP.  XIV. 

"  to  complete  the  scheme  of  nature."  But  this  is  not  an 
explanation,  merely  a  re-statement  of  the  fact.  Nor 
is  it  consistent  with  itself;  thus  the  boa-constrictor  has 
rudiments  of  hind-limbs  and  of  a  pelvis,  and  if  it  be 
said  that  these  bones  have  been  retained  "  to  complete 
the  scheme  of  nature,"  why,  as  Professor  Weismann 
asks,  have  they  not  been  retained  by  other  snakes,  which 
do  not  possess  even  a  vestige  of  these  same  bones?  What 
would  be  the  thought  of  an  astronomer  who  maintained 
that  the  satellites  revolve  in  elliptic  courses  round  their 
planets  "  for  the  sake  of  symmetry,"  because  the  planets 
thus  revolve  round  the  sun?  An  eminent  physiologist 
accounts  for  the  presence  of  rudimentary  organs,  by 
supposing  that  they  serve  to  excrete  matter  in  excess, 
or  matter  injurious  to  the  system;  but  can  we  suppose 
that  the  minute  papilla,  which  often  represents  the 
pistil  in  male  flowers,  and  which  is  formed  of  mere 
cellular  tissue,  can  thus  act?  Can  we  suppose  that 
rudimentary  teeth,  which  are  subsequently  absorbed, 
are  beneficial  to  the  rapidly  growing  embryonic  calf  by 
removing  matter  so  precious  as  phosphate  of  lime? 
When  a  man's  fingers  have  been  amputated,  imperfect 
nails  have  been  known  to  appear  on  the  stumps,  and  I 
could  as  soon  believe  that  these  vestiges  of  nails  are  de- 
veloped in  order  to  excrete  horny  matter,  as  that  the 
rudimentary  nails  on  the  fin  of  the  manatee  have  been 
developed  for  this  same  purpose. 

On  the  view  of  descent  with  modification,  the  origin 
of  rudimentary  organs  is  comparatively  simple;  and  we 
can  understand  to  a  large  extent  the  laws  governing 
their  imperfect  development.  We  have  plenty  of  cases 
of  rudimentary  organs  in  our  domestic  productions, — as 
the  stump  of  a  tail  in  tailless  breeds, — the  vestige  of  an 


CHAP.  XIV.]         AND  ABORTED  ORGANS.  261 

ear  in  earless  breeds  of  sheep, — the  reappearance  of 
minute  dangling  horns  in  hornless  breeds  of  cattle, 
more  especially,  according  to  Youatt,  in  young  animals, 
— and  the  state  of  the  whole  flower  in  the  cauliflower. 
We  often  see  rudiments  of  various  parts  in  monsters; 
but  I  doubt  whether  any  of  these  cases  throw  light  on 
the  origin  of  rudimentary  organs  in  a  state  of  nature, 
further  than  by  showing  that  rudiments  can  be  pro- 
duced; for  the  balance  of  evidence  clearly  indicates  that 
species  under  nature  do  not  undergo  great  and  abrupt 
changes.  But  we  learn  from  the  study  of  our  domestic 
productions  that  the  disuse  of  parts  leads  to  their  re- 
duced size;  and  that  the  result  is  inherited. 

It  appears  probable  that  disuse  has  been  the  main 
agent  in  rendering  organs  rudimentary.  It  would  at 
first  lead  by  slow  steps  to  the  more  and  more  complete 
reduction  of  a  part,  until  at  last  it  became  rudimentary, 
— as  in  the  case  of  the  eyes  of  animals  inhabiting  dark 
caverns,  and  of  the  wings  of  birds  inhabiting  oceanic 
islands,  which  have  seldom  been  forced  by  beasts  of  prey 
to  take  flight,  and  have  ultimately  lost  the  power  of 
flying.  Again,  an  organ,  useful  under  certain  condi- 
tions, might  become  injurious  under  others,  as  with  the 
wings  of  beetles  living  on  small  and  exposed  islands;  and 
in  this  case  natural  selection  will  have  aided  in  reducing 
the  organ,  until  it  was  rendered  harmless  and  rudi- 
mentary. 

Any  change  in  structure  and  function,  which  can  be 
effected  by  small  stages,  is  within  the  power  of  natural 
selection;  so  that  an  organ  rendered,  through  changed 
habits  of  life,  useless  or  injurious  for  one  purpose,  might 
be  modified  and  used  for  another  purpose.  An  organ 
might,  also,  be  retained  for  one  alone  of  its  former  func- 


262  RUDIMENTARY,   ATROPHIED,     [CHAP.  XIV. 

tions.  Organs,  originally  formed  by  the  aid  of  natural 
selection,  when  rendered  useless  may  well  be  variable, 
for  their  variations  can  no  longer  be  checked  by  natural 
selection.  All  this  agrees  well  with  what  we  see  under 
nature.  Moreover,  at  whatever  period  of  life  either  dis- 
use or  selection  reduces  an  organ,  and  this  will  generally 
be  when  the  being  has  come  to  maturity  and  has  to 
exert  its  full  powers  of  action,  the  principle  of  inherit- 
ance at  corresponding  ages  will  tend  to  reproduce  the 
organ  in  its  reduced  state  at  the  same  mature  age,  but 
will  seldom  effect  it  in  the  embryo.  Thus  we  can  un- 
derstand the  greater  size  of  rudimentary  organs  in  the 
embryo  relatively  to  the  adjoining  parts,  and  their 
lesser  relative  size  in  the  adult.  If,  for  instance,  the 
digit  of  an  adult  animal  was  used  less  and  less  during 
many  generations,  owing  to  some  change  of  habits,  or  if 
an  organ  or  gland  was  less  and  less  functionally  exercised, 
we  may  infer  that  it  would  become  reduced  in  size  in  the 
adult  descendants  of  this  animal,  but  would  retain  nearly 
its  original  standard  of  development  in  the  embryo. 

There  remains,  however,  this  difficulty.  After  an 
organ  has  ceased  being  used,  and  has  become  in  con- 
sequence much  reduced,  how  can  it  be  still  further  re- 
duced in  size  until  the  merest  vestige  is  left;  and  how 
can  it  be  finally  quite  obliterated?  It  is  scarcely  pos- 
sible that  disuse  can  go  on  producing  any  further  effect 
after  the  organ  has  once  been  rendered  functionless. 
Some  additional  explanation  is  here  requisite  which  I 
cannot  give.  If,  for  instance,  it  could  be  proved  that 
every  part  of  the  organisation  tends  to  vary  in  a  greater 
degree  towards  diminution  than  towards  augmentation 
of  size,  then  we  should  be  able  to  understand  how  an 
organ  which  has  become  useless  would  be  rendered,  in- 


CHAP.  XIV.]          AND  ABORTED  ORGANS.  263 

dependency  of  the  effects  of  disuse,  rudimentary  and 
would  at  last  be  wholly  suppressed;  for  the  variations 
towards  diminished  size  would  no  longer  be  checked  by 
natural  selection.  The  principle  of  the  economy  of 
growth,  explained  in  a  former  chapter,  by  which  the 
materials  forming  any  part,  if  not  useful  to  the  pos- 
sessor, are  saved  as  far  as  possible,  will  perhaps  come 
into  play  in  rendering  a  useless  part  rudimentary.  But 
this  principle  will  almost  necessarily  be  confined  to  the 
earlier  stages  of  the  process  of  reduction;  for  we  cannot 
suppose  that  a  minute  papilla,  for  instance,  representing 
in  a  male  flower  the  pistil  of  the  female  flower,  and 
formed  merely  of  cellular  tissue,  could  be  further  re- 
duced or  absorbed  for  the  sake  of  economising  nutriment. 
Finally,  as  rudimentary  organs,  by  whatever  steps 
they  may  have  been  degraded  into  their  present  useless 
condition,  are  the  record  of  a  former  state  of  things,  and 
have  been  retained  solely  through  the  power  of  inherit- 
ance,— we  can  understand,  on  the  genealogical  view  of 
classification,  how  it  is  that  systematists,  in  placing 
organisms  in  their  proper  places  in  the  natural  system, 
have  often  found  rudimentary  parts  as  useful  as,  or  even 
sometimes  more  useful  than,  parts  of  high  physiologi- 
cal importance.  Eudimentary  organs  may  be  compared 
with  the  letters  in  a  word,  still  retained  in  the  spelling, 
but  become  useless  in  the  pronunciation,  but  which  serve 
as  a  clue  for  its  derivation.  On  the  view  of  descent 
with  modification,  we  may  conclude  that  the  existence 
of  organs  in  a  rudimentary,  imperfect,  and  useless  condi- 
tion, or  quite  aborted,  far  from  presenting  a  strange 
difficulty,  as  they  assuredly  do  on  the  old  doctrine  of 
creation,  might  even  have  been  anticipated  in  accordance 
with  the  views  here  explained. 


2G4  SUMMARY.  [CHAP.  XIV. 


Summary. 

In  this  chapter  I  have  attempted  to  show,  that  the 
arrangement  of  all  organic  beings  throughout  all  time 
in  groups  under  groups — that  the  nature  of  the  relation- 
ships by  which  all  living  and  extinct  organisms  are 
united  by  complex,  radiating,  and  circuitous  lines  of 
affinities  into  a  few  grand  classes, — the  rules  followed 
and  the  difficulties  encountered  by  naturalists  in  their 
classifications, — the  value  set  upon  characters,  if  con- 
stant and  prevalent,  whether  of  high  or  of  the  most  tri- 
fling importance,  or,  as  with  rudimentary  organs,  of  no 
importance, — the  wide  opposition  in  value  between  an- 
alogical or  adaptive  characters,  and  characters  of  true 
affinity;  and  other  such  rules; — all  naturally  follow  if 
we  admit  the  common  parentage  of  allied  forms,  to- 
gether with  their  modification  through  variation  and 
natural  selection,  with  the  contingencies  of  extinction 
and  divergence  of  character.  In  considering  this  view 
of  classification,  it  should  be  borne  in  mind  that  the  ele- 
ment of  descent  has  been  universally  used  in  ranking  to- 
gether the  sexes,  ages,  dimorphic  forms,  and  acknowl- 
edged varieties  of  the  same  species,  however  much  they 
may  differ  from  each  other  in  structure.  If  we  extend 
the  use  of  this  element  of  descent, — the  one  certainly 
known  cause  of  similarity  in  organic  beings, — we  shall 
understand  what  is  meant  by  the  Natural  System:  it  is 
genealogical  in  its  attempted  arrangement,  with  the 
grades  of  acquired  difference  marked  by  the 
terms,  varieties,  species,  genera,  families,  orders,  and 
classes. 

On  this  same  view  of  descent  with  modification,  most 


CHAP.  XIV.]  SUMMARY.  265 

of  the  great  facts  in  Morphology  become  intelligible, — 
whether  we  look  to  the  same  pattern  displayed  by  the 
different  species  of  the  same  class  in  their  homologous 
organs,  to  whatever  purpose  applied;  or  to  the  serial  and 
lateral  homologies  in  each  individual  animal  and 
plant. 

On  the  principle  of  successive  slight  variations,  not 
necessarily  or  generally  supervening  at  a  very  early 
period  of  life,  and  being  inherited  at  a  corresponding 
period,  we  can  understand  the  leading  facts  in  Embry- 
ology; namely,  the  close  resemblance  in  the  individual 
embryo  of  the  parts  which  are  homologous,  and  which 
when  matured  become  widely  different  in  structure  and 
function;  and  the  resemblance  of  the  homologous  parts 
or  organs  in  allied  though  distinct  species,  though  fitted 
in  the  adult  state  for  habits  as  different  as  is  possible. 
Larva?  are  active  embryos,  which  have  been  specially 
modified  in  a  greater  or  less  degree  in  relation  to  their 
habits  of  life,  with  their  modifications  inherited  at  a 
corresponding  early  age.  On  these  same  principles, — 
and  bearing  in  mind  that  when  organs  are  reduced  in 
size,  either  from  disuse  or  through  natural  selection,  it 
will  generally  be  at  that  period  of  life  when  the  being 
has  to  provide  for  its  own  wants,  and  bearing  in  mind 
how  strong  is  the  force  of  inheritance — the  occurrence 
of  rudimentary  organs  might  even  have  been  anticipated. 
The  importance  of  embryological  characters  and  of  rudi- 
mentary organs  in  classification  is  intelligible,  on  the 
view  that  a  natural  arrangement  must  be  genealogical. 

Finally,  the  several  classes  of  facts  which  have  been 
considered  in  this  chapter,  seem  to  me  to  proclaim  so 
plainly,  that  the  innumerable  species,  genera  and  fami- 
lies, with  which  this  world  is  peopled,  are  all  descended, 
43 


266  SUMMARY.  [CHAP.  XIV. 

each  within  its  own  class  or  group,  from  common 
parents,  and  have  all  been  modified  in  the  course  of  de- 
scent, that  I  should  without  hesitation  adopt  this  view, 
even  if  it  were  unsupported  by  other  facts  or  arguments. 


CHAP.  XV.]  RECAPITULATION.  267 


CHAPTER   XV. 

RECAPITULATION   AND   CONCLUSION. 

Recapitulation  of  the  objections  to  the  theory  of  Natural  Selection 
— Recapitulation  of  the  general  and  special  circumstances  in  its 
favour — Causes  of  the  general  belief  in  the  immutability  of 
species — How  far  the  theory  of  Natural  Selection  may  be  ex- 
tended— Effects  of  its  adoption  on  the  study  of  Natural  History 
— Concluding  Remarks. 

As  this  whole  volume  is  one  long  argument,  it  may 
be  convenient  to  the  reader  to  have  the  leading  facts 
and  inferences  briefly  recapitulated. 

That  many  and  serious  objections  may  be  advanced 
against  the  theory  of  descent  with  modification  through 
variation  and  natural  selection,  I  do  not  deny.  I  have 
endeavoured  to  give  to  them  their  full  force.  Nothing 
at  first  can  appear  more  difficult  to  believe  than  that 
the  more  complex  organs  and  instincts  have  been  per- 
fected, not  by  means  superior  to,  though  analogous  with, 
human  reason,  but  by  the  accumulation  of  innumerable 
slight  variations,  each  good  for  the  individual  possessor. 
Nevertheless,  this  difficulty,  though  appearing  to  our 
imagination  insuperably  great,  cannot  be  considered 
real  if  we  admit  the  following  propositions,  namely, 
that  all  parts  of  the  organisation  and  instincts  offer,  at 
least,  individual  differences — that  there  is  a  struggle  for 
existence  leading  to  the  "preservation  of  profitable  devia- 
tions of  structure  or  instinct — and,  lastly,  that  grada- 


268  RECAPITULATION.  [CHAP.  XV. 

tions  in  the  state  of  perfection  of  each  organ  may  have 
existed,  each  good  of  its  kind.  The  truth  of  these 
propositions  cannot,  I  think,  be  disputed. 

It  is,  no  doubt,  extremely  difficult  even  to  conjecture 
by  what  gradations  many  structures  have  been  perfected, 
more  especially  amongst  broken  and  failing  groups  of 
organic  beings,  which  have  suffered  much  extinction, 
but  we  see  so  many  strange  gradations  in  nature,  that 
we  ought  to  be  extremely  cautious  in  saying  that  any 
organ  or  instinct,  or  any  whole  structure,  could  not  have 
arrived  at  its  present  state  by  many  graduated  steps. 
There  are,  it  must  be  admitted,  cases  of  special  difficulty 
opposed  to  the  theory  of  natural  selection;  and  one  of 
the  most  curious  of  these  is  the  existence  in  the  same 
community  of  two  or  three  denned  castes  of  workers  or 
sterile  female  ants;  but  I  have  attempted  to  show  how 
these  difficulties  can  be  mastered. 

With  respect  to  the  almost  universal  sterility  of 
species  when  first  crossed,  which  forms  so  remarkable  a 
contrast  with  the  almost  universal  fertility  of  varieties 
when  crossed,  I  must  refer  the  reader  to  the  recapitula- 
tion of  the  facts  given  at  the  end  of  the  ninth  chapter, 
which  seem  to  me  conclusively  to  show  that  this  sterility 
is  no  more  a  special  endowment  than  is  the  incapacity  of 
two  distinct  kinds  of  trees  to  be  grafted  together;  but 
that  it  is  incidental  on  differences  confined  to  the  repro- 
ductive systems  of  the  intercrossed  species.  We  see  the 
truth  of  this  conclusion  in  the  vast  difference  in  the 
results  of  crossing  the  same  two  species  reciprocally, — 
that  is,  when  one  species  is  first  used  as  the  father  and 
then  as  the  mother.  Analogy  from  the  consideration  of 
dimorphic  and  trimorphic  plants  clearly  leads  to  the 
same  conclusion,  for  when  the  forms  are  illegitimately 


CHAP.  XV.]  RECAPITULATION.  269 

united,  they  yield  few  or  no  seed,  and  their  offspring  are 
more  or  less  sterile;  and  these  forms  belong  to  the  same 
undoubted  species,  and  differ  from  each  other  in  no  re- 
spect except  in  their  reproductive  organs  and  functions. 

Although  the  fertility  of  varieties  when  intercrossed 
and  of  their  mongrel  offspring  has  been  asserted  by  so 
many  authors  to  be  universal,  this  cannot  be  considered 
as  quite  correct  after  the  facts  given  on  the  high 
authority  of  Gartner  and  Kolreuter.  Most  of  the  varie- 
ties which  have  been  experimented  on  have  been  pro- 
duced under  domestication;  and  as  domestication  (I  do 
not  mean  mere  confinement)  almost  certainly  tends  to 
eliminate  that  sterility  which,  judging  from  analogy, 
would  have  affected  the  parent-species  if  intercrossed,  we 
ought  not  to  expect  that  domestication  would  likewise 
induce  sterility  in  their  modified  descendants  when 
crossed.  This  elimination  of  sterility  apparently  follows 
from  the  same  cause  which  allows  our  domestic  animals 
to  breed  freely  under  diversified  circumstances;  and  this 
again  apparently  follows  from  their  having  been  gradu- 
ally accustomed  to  frequent  changes  in  their  conditions 
of  life. 

A  double  and  parallel  series  of  facts  seems  to  throw 
much  light  on  the  sterility  of  species,  when  first  crossed, 
and  of  their  hybrid  offspring.  On  the  one  side,  there  is 
good  reason  to  believe  that  slight  changes  in  the  con- 
ditions of  life  give  vigour  and  fertility  to  all  organic 
beings.  We  know  also  that  a  cross  between  the  distinct 
individuals  of  the  same  variety,  and  between  distinct 
varieties,  increases  the  number  of  their  offspring,  and 
certainly  gives  to  them  increased  size  and  vigour.  This 
is  chiefly  owing  to  the  forms  which  are  crossed  having 
been  exposed  to  somewhat  different  conditions  of  life; 


270  RECAPITULATION.  [CHAP.  XV. 

for  I  have  ascertained  by  a  laborious  series  of  experi- 
ments that  if  all  the  individuals  of  the  same  variety 
be  subjected  during  several  generations  to  the  same 
conditions,  the  good  derived  from  crossing  is  often  much 
diminished  or  wholly  disappears.  This  is  one  side  of 
the  case.  On  the  other  side,  we  know  that  species  which 
have  long  been  exposed  to  nearly  uniform  conditions, 
when  they  are  subjected  under  confinement  to  new  and 
greatly  changed  conditions,  either  perish,  or  if  they  sur- 
vive, are  rendered  sterile,  though  retaining  perfect 
health.  This  does  not  occur,  or  only  in  a  very  slight  de- 
gree, with  our  domesticated  productions,  which  have 
long  been  exposed  to  fluctuating  conditions.  Hence 
when  we  find  that  hybrids  produced  by  a  cross  between 
two  distinct  species  are  few  in  number,  owing  to  their 
perishing  soon  after  conception  or  at  a  very  early  age, 
or  if  surviving  that  they  are  rendered  more  or  less  sterile, 
it  seems  highly  probable  that  this  result  is  due  to  their 
having  been  in  fact  subjected  to  a  great  change  in  their 
conditions  of  life,  from  being  compounded  of  two  dis- 
tinct organisations.  He  who  will  explain  in  a  definite 
manner  why,  for  instance,  an  elephant  or  a  fox  will  not 
breed  under  confinement  in  its  native  country,  whilst 
the  domestic  pig  or  dog  will  breed  freely  under  the  most 
diversified  conditions,  will  at  the  same  time  be  able  to 
give  a  definite  answer  to  the  question  why  two  distinct 
species,  when  crossed,  as  well  as  their  hybrid  offspring, 
are  generally  rendered  more  or  less  sterile,  whilst  two 
domesticated  varieties  when  crossed  and  their  mongrel 
offspring  are  perfectly  fertile. 

Turning  to  geographical  distribution,  the  difficulties 
encountered  on  the  theory  of  descent  with  modification 
are  serious  enough.  All  the  individuals  of  the  same 


CEAP.  XV.]  RECAPITULATION.  271 

species,  and  all  the  species  of  the  same  genus,  or  even 
higher  group,  are  descended  from  common  parents;  and 
therefore,  in  however  distant  and  isolated  parts  of  the 
world  they  may  now  be  found,  they  must  in  the  course 
of  successive  generations  have  travelled  from  some  one 
point  to  all  the  others.  We  are  often  wholly  unable  even 
to  conjecture  how  this  could  have  been  effected.  Yet, 
as  we  have  reason  to  believe  that  some  species  have  re- 
tained the  same  specific  form  for  very  long  periods  of 
time,  immensely  long  as  measured  by  years,  too  much 
stress  ought  not  to  be  laid  on  the  occasional  wide  diffu- 
sion of  the  same  species;  for  during  very  long  periods 
there  will  always  have  been  a  good  chance  for  wide 
migration  by  many  means.  A  broken  or  interrupted 
range  may  often  be  accounted  for  by  the  extinction  of 
the  species  in  the  intermediate  regions.  It  cannot  be 
denied  that  we  are  as  yet  very  ignorant  as  to  the  full 
extent  of  the  various  climatal  and  geographical  changes 
which  have  affected  the  earth  during  modern  periods; 
and  such  changes  will  often  have  facilitated  migration. 
As  an  example,  I  have  attempted  to  show  how  potent 
has  been  the  influence  of  the  Glacial  period  on  the  dis- 
tribution of  the  same  and  of  allied  species  throughout 
the  world.  We  are  as  yet  profoundly  ignorant  of  the 
many  occasional  means  of  transport.  With  respect  to 
distinct  species  of  the  same  genus  inhabiting  distant 
and  isolated  regions,  as  the  process  of  modification  has 
necessarily  been  slow,  all  the  means  of  migration  will 
have  been  possible  during  9  very  long  period;  and  con- 
sequently the  difficulty  of  the  wide  diffusion  of  the 
species  of  the  same  genus  is  in  some  degree  lessened. 

As  according  to  the  theory  of  natural  selection  an 
interminable  number  of  intermediate  forms  must  have 


272  RECAPITULATION.  [CHAP.  XV. 

existed,  linking  together  all  the  species  in  each  group  by 
gradations  as  fine  as  are  our  existing  varieties,  it  may  be 
asked,  Why  do  we  not  see  these  linking  forms  all  around 
us?  Why  are  not  all  organic  beings  blended  together 
in  an  inextricable  chaos?  With  respect  to  existing  forms, 
we  should  remember  that  we  have  no  right  to  expect 
(excepting  in  rare  cases)  to  discover  directly  connecting 
links  between  them,  but  only  between  each  and  some 
extinct  and  supplanted  form.  Even  on  a  wide  area, 
which  has  during  a  long  period  remained  continuous, 
and  of  which  the  climatic  and  other  conditions  of  life 
change  insensibly  in  proceeding  from  a  district  occupied 
by  one  species  into  another  district  occupied  by  a  closely 
allied  species,  we  have  no  just  right  to  expect  often  to 
find  intermediate  varieties  in  the  intermediate  zones. 
For  we  have  reason  to  believe  that  only  a  few  species 
of  a  genus  ever  undergo  change;  the  other  species  be- 
coming utterly  extinct  and  leaving  no  modified  progeny. 
Of  the  species  which  do  change,  only  a  few  within  the 
same  country  change  at  the  same  time;  and  all  modi- 
fications are  slowly  effected.  I  have  also  shown  that  the 
intermediate  varieties  which  probably  at  first  existed 
in  the  intermediate  zones,  would  be  liable  to  be  sup- 
planted by  the  allied  forms  on  either  hand;  for  the  lat- 
ter, from  existing  in  greater  numbers,  would  generally 
be  modified  and  improved  at  a  quicker  rate  than  the 
intermediate  varieties,  which  existed  in  lesser  numbers; 
so  that  the  intermediate  varieties  would,  in  the  long 
run,  be  supplanted  and  exterminated. 

On  this  doctrine  of  the  extermination  of  an  infini- 
tude of  connecting  links,  between  the  living  and  extinct 
inhabitants  of  the  world,  and  at  each  successive  period 
between  the  extinct  and  still  older  species,  why  is  not 


CHAP.  XV.]  RECAPITULATION.  273 

every  geological  formation  charged  with  such  links? 
Why  does  not  every  collection  of  fossil  remains  afford 
plain  evidence  of  the  gradation  and  mutation  of  the 
forms  of  life?  Although  geological  research  has  un- 
doubtedly revealed  the  former  existence  of  many  links, 
bringing  numerous  forms  of  life  much  closer  together,  it 
does  not  yield  the  infinitely  many  fine  gradations  be- 
tween past  and  present  species  required  on  the  theory; 
and  this  is  the  most  obvious  of  the  many  objections  which 
may  be  urged  against  it.  Why,  again,  do  whole  groups 
of  allied  species  appear,  though  this  appearance  is  often 
false,  to  have  come  in  suddenly  on  the  successive  geologi- 
cal stages?  Although  we  now  know  that  organic  be- 
ings appeared  on  this  globe,  at  a  period  incalculably  re- 
mote, long  before  the  lowest  bed  of  the  Cambrian  system 
was  deposited,  why  do  we  not  find  beneath  this  system 
great  piles  of  strata  stored  with  the  remains  of  the  pro- 
genitors of  the  Cambrian  fossils?  For  on  the  theory, 
such  strata  must  somewhere  have  been  deposited  at 
these  ancient  and  utterly  unknown  epochs  of  the  world's 
history. 

I  can  answer  these  questions  and  objections  only  on 
the  supposition  that  the  geological  record  is  far  more  im- 
perfect than  most  geologists  believe.  The  number  of 
specimens  in  all  our  museums  is  absolutely  as  nothing 
compared  with  the  countless  generations  of  countless 
species  which  have  certainly  existed.  The  parent-form 
of  any  two  or  more  species  would  not  be  in  all  its  char- 
acters directly  intermediate  between  its  modified  off- 
spring, any  more  than  the  rock-pigeon  is  directly  inter- 
mediate in  crop  and  tail  between  its  descendants,  the 
pouter  and  fantail  pigeons.  We  should  not  be  able  to 
recognise  a  species  as  the  parent  of  another  and  modi- 


274  RECAPITULATION.  {CHAP.  XV. 

fied  species,  if  we  were  to  examine  the  two  ever  so  close- 
ly, unless  we  possessed -most  of  the  intermediate  links; 
and  owing  to  the  imperfection  of  the  geological  record, 
we  have  no  just  right  to  expect  to  find  so  many  links. 
If  two  or  three,  or  even  more  linking  forms  were  dis- 
covered, they  would  simply  be  ranked  by  many  natu- 
ralists as  so  many  new  species,  more  especially  if  found 
in  different  geological  sub-stages,  let  their  differences 
be  ever  so  slight.  Numerous  existing  doubtful  forms 
could  be  named  which  are  probably  varieties;  but  who 
will  pretend  that  in  future  ages  so  many  fossil  links 
will  be  discovered,  that  naturalists  will  be  able  to  decide 
whether  or  not  these  doubtful  forms  ought  to  be  called 
varieties?  *0nly  a  small  portion  of  the  world  has  been 
geologically  explored.  Only  organic  beings  of  certain 
classes  can  be  preserved  in  a  fossil  condition,  at  least 
in  any  great  number.  Many  species  when  once  formed 
never  undergo  any  further  change  but  become  extinct 
without  leaving  modified  descendants;  and  the  periods, 
during  which  species  have  undergone  modification, 
though  long  as  measured  by  years,  have  probably  been 
short  in  comparison  with  the  periods  during  which 
they  retain  the  same  form.  It  is  the  dominant  and 
widely  ranging  species  which  vary  most  frequently  and 
vary  most,  and  varieties  are  often  at  first  local — both 
causes  rendering  the  discovery  of  intermediate  links  in 
any  one  formation  less  likely.  Local  varieties  will  not 
spread  into  other  and  distant  regions  until  they  are 
considerably  modified  and  improved;  and  when  they 
have  spread,  ajid  are  discovered  in  a  geological  forma- 
tion, they  appear  as  if  suddenly  created  there,  and  will 
be  simply  classed  as  new  species.  Most  formations  have 
•been  intermittent  in  their  accumulation;  and  their  dura- 


CIIAF.  XV.]  RECAPITULATION.  275 

tion  has  probably  been  shorter  than  the  average  dura- 
tion of  specific  forms.  Successive  formations  are  in 
most  cases  separated  from  each  other  by  blank  intervals 
of  time  of  great  length;  for  fossiliferous  formations  thick 
enough  to  resist  future  degradation  can  as  a  general  rule 
be  accumulated  only  where  much  sediment  is  deposited 
on  the  subsiding  bed  of  the  sea.  During  the  alternate 
periods  of  elevation  and  of  stationary  level  the  record 
will  generally  be  blank.  During  these  latter  periods 
there  will  probably  be  more  variability  in  the  forms  of 
life;  during  periods  of  subsidence,  more  extinction. 

With  respect  to  the  absence  of  strata  rich  in  fossils 
beneath  the  Cambrian  formation,  I  can  recur  only  to 
the  hypothesis  given  in  the  tenth  chapter;  namely,  that 
though  our  continents  and  oceans  have  endured  for  an 
encrmous  period  in  nearly  their  present  relative  posi- 
tions, we  have  no  reason  to  assume  that  this  has  always 
been  the  case;  consequently  formations  much  older  than 
any  now  known  may  lie  buried  beneath  the  great  oceans. 
With  respect  to  the  lapse  of  time  not  having  been  suffi- 
cient since  our  planet  was  consolidated  for  the  assumed 
amount  of  organic  change,  and  this  objection,  as  urged 
by  Sir  William  Thompson,  is  probably  one  of  the  gravest 
as  yet  advanced,  I  can  only  say,  firstly,  that  we  do  not 
know  at  what  rate  species  change  as  measured  by  years, 
and  secondly,  that  ma'ny  philosophers  are  not  as  yet 
willing  to  admit  that  we  know  enough  of  the  constitu- 
tion of  the  universe  and  of  the  interior  of  our  globe  to 
speculate  with  safety  on  its  past  duration. 

That  the  geological  record  is  imperfect  all  will  admit; 
but  that  it  is  imperfect  to  the  degree  required  by  our 
theory,  few  will  be  inclined  to  admit.  If  we  look  to 
long  enough  intervals  of  time,  geology  plainly  declares 


276  RECAPITULATION.  [CHAP.  XV. 

that  species  have  all  changed;  and  they  have  changed 
in  the  manner  required  by  the  theory,  for  they  have 
changed  slowly  and  in  a  graduated  manner.  We  clearly 
see  this  in  the  fossil  remains  from  consecutive  formations 
invariably  being  much  more  closely  related  to  each  other, 
than  are  the  fossils  from  widely  separated  formations. 

Such  is  the  sum  of  the  several  chief  objections  and 
difficulties  which  may  be  justly  urged  against  the  theory; 
and  I  have  now  briefly  recapitulated  the  answers  and 
explanations  which,  as  far  as  I  can  see,  may  be  given. 
I  have  felt  these  difficulties  far  too  heavily  during  many 
years  to  doubt  their  weight.  But  it  deserves  especial 
notice  that  the  more  important  objections  relate  to  ques- 
tions on  which  we  are  confessedly  ignorant;  nor  do 
we  know  how  ignorant  we  are.  We  do  not  know  all 
the  possible  transitional  gradations  between  the  simplest 
and  the  most  perfect  organs;  it  cannot  be  pretended 
that  we  know  all  the  varied  means  of  Distribution  dur- 
ing the  long  lapse  of  years,  or  that  we  know  how  im- 
perfect is  the  Geological  Record.  Serious  as  these  sev- 
eral objections  are,  in  my  judgment  they  are  by  no  means 
sufficient  to  overthrow  the  theory  of  descent  with  sub- 
sequent modification. 

Now  let  us  turn  to  the  other  side  of  the  argument. 
Under  domestication  we  see  much  variability,  caused,  or 
at  least  excited,  by  changed  conditions  of  life;  but  often 
in  so  obscure  a  manner,  that  we  are  tempted  to  consider 
the  variations  as  spontaneous.  Variability  is  governed 
by  many  complex  laws, — by  correlated  growth,  compen- 
sation, the  increased  use  and  disuse  of  parts,  and  the 
definite  action  of  the  surrounding  conditions.  There  is 
much  difficulty  in  ascertaining  how  largely  our  domestic 


CHAP.  XV.]  RECAPITULATION.  277 

productions  have  been  modified;  but  we  may  safely  in- 
fer that  the  amount  has  been  large,  and  that  modifica- 
tions can  be  inherited  for  long  periods.  As  long  as  the 
conditions  of  life  remain  the  same,  we  have  reason  to 
believe  that  a  modification,  which  has  already  been, 
inherited  for  many  generations,  may  continue  to  be 
inherited  for  an  almost  infinite  number  of  generations. 
On  the  other  hand,  we  have  evidence  that  variability 
when  it  has  once  come  into  play,  does  not  cease  under 
domestication  for  a  very  long  period;  nor  do  we  know 
that  it  ever  ceases,  for  new  varieties  are  still  occasionally 
produced  by  our  oldest  domesticated  productions. 

Variability  is  not  actually  caused  by  man;  he  only 
unintentionally  exposes  organic  beings  to  new  condi- 
tions of  life,  and  then  nature  acts  on  the  organisation 
and  causes  it  to  vary.  But  man  can  and  does  select  the 
variations  given  to  him  by  nature,  and  thus  accumulates 
them  in  any  desired  manner.  He  thus  adapts  animals 
and  plants  for  his  own  benefit  or  pleasure.  He  may 
do  this  methodically,  or  he  may  do  it  unconsciously  by 
preserving  the  individuals  most  useful  or  pleasing  to 
him  without  any  intention  of  altering  the  breed.  It  is 
certain  that  he  can  largely  influence  the  character  of  a 
breed  by  selecting,  in  each  successive  generation,  indi- 
vidual differences  so  slight  as  to  be  inappreciable  except 
by  an  educated  eye.  This  unconscious  process  of  selec- 
tion has  been  the  great  agency  in  the  formation  of  the 
most  distinct  and  useful  domestic  breeds.  That  many 
breeds  produced  by  man  have  to  a  large  -extent  the 
character  of  natural  species,  is  shown  by  the  inextric- 
able doubts  whether  many  of  them  are  varieties  or 
aboriginally  distinct  species. 

There  is  no  reason  why  the  principles  which  have 


278  RECAPITULATION.  [CHAP.  XV> 

acted  so  efficiently  under  domestication  should  not  have 
acted  under  nature.  In  the  survival  of  favoured  indi- 
viduals and  races,  during  the  constantly-recurrent 
Struggle  for  Existence,  we  see  a  powerful  and  ever- 
acting  form  of  Selection.  The  struggle  for  existence 
inevitably  follows  from  the  high  geometrical  ratio  of 
increase  which  is  common  to  all  organic  beings.  This 
high  rate  of  increase  is  proved  by  calculation, — by  the 
rapid  increase  of  many  animals  and  plants  during  a 
succession  of  peculiar  seasons,  and  when  naturalised  in 
new  countries.  More  individuals  are  born  than  can 
possibly  survive.  A  grain  in  the  balance  may  determine 
which  individuals  shall  live  and  Avhich  shall  die, — which 
variety  or  species  shall  increase  in  number,  and  which 
shall  decrease,  or  finally  become  extinct.  As  the  indi- 
viduals of  the  same  species  come  in  all  respects  into  the 
closest  competition  with  each  other,  the  struggle  will 
generally  be  most  severe  between  them;  it  will  be  al- 
most equally  severe  between  the  varieties  of  the  same 
species,  and  next  in  severity  between  the  species  of  the 
same  genus.  On  the  other  hand  the  struggle  will  often 
be  severe  between  beings  remote  in  the  scale  of  nature. 
The  slightest  advantage  in  certain  individuals,  at  any 
age  or  during  any  season,  over  those  with  which  they 
come  into  competition,  or  better  adaptation  in  however 
slight  a  degree  to  the  surrounding  physical  conditions, 
will,  in  the  long  run,  turn  the  balance. 

With  animals  having  separated  sexes,  there  will  be 
in  most  cases  a  struggle  between  the  males  for  the  pos- 
session of  the  females.  The  most  vigorous  males,  or 
those  which  have  most  successfully  struggled  with  their 
conditions  of  life,  will  generally  leave  most  progeny. 
But  success  will  often  depend  on  the  males  having  spe- 


CHAP.  XV.]  RECAPITULATION.  279 

cial  weapons,  or  means  of  defence,  or  charms;  and  a 
slight  advantage  will  lead  to  victory. 

As  geology  plainly  proclaims  that  each  land  has 
undergone  great  physical  changes,  we  might  have  ex- 
pected to  find  that  organic  beings  have  varied  under 
nature,  in  the  same  way  as  they  have  varied  under  do- 
mestication. And  if  there  has  been  any  variability 
under  nature,  it  would  be  an  unaccountable  fact  if  natu- 
ral selection  had  not  come  into  play.  It  has  often  been 
asserted,  but  the  assertion  is  incapable  of  proof,  that  the 
amount  of  variation  under  nature  is  a  strictly  limited 
quantity.  Man,  though  acting  on  external  characters 
alone  and  often  capriciously,  can  produce  within  a  short 
period  a  great  result  by  adding  up  mere  individual  dif- 
ferences in  his  domestic  productions;  and  every  one  ad- 
mits that  species  present  individual  differences.  But, 
besides  such  differences,  all  naturalists  admit  that  natu- 
ral varieties  exist,  which  are  considered  sufficiently  dis- 
tinct to  be  worthy  of  record  in  systematic  works.  No 
one  has  drawn  any  clear  distinction  between  individual 
differences  and  slight  varieties;  or  between  more  plainly 
marked  varieties  and  sub-species,  and  species.  On  sepa- 
rate continents,  and  on  different  parts  of  the  same  conti- 
nent when  divided  by  barriers  of  any  kind,  and  on  out- 
lying islands,  what  a  multitude  of  forms  exist,  which 
some  experienced  naturalists  rank  as  varieties,  others  as 
geographical  races  or  sub-species,  and  others  as  distinct, 
though  closely  allied  species! 

If  then,  animals  and  plants  do  vary,  let  it  be  ever  so 
slightly  or  slowly,  why  should  not  variations  or  indi- 
vidual differences,  which  are  in  any  way  beneficial,  be 
preserved  and  accumulated  through  natural  selection,  or 
the  survival  of  the  fittest?  If  man  can  by  patience 


280  RECAPITULATION.  [CHAP.  XV. 

select  variations  useful  to  him,  why,  under  changing 
and  complex  conditions  of  life,  should  not  variations 
useful  to  nature's  living  products  often  arise,  and  be 
preserved  or  selected?  What  limit  can  be  put  to  this 
power,  acting  during  long  ages  and  rigidly  scrutinising 
the  whole  constitution,  structure,  and  habits  of  each 
creature, — favouring  the  good  and  rejecting  the  bad?  I 
can  see  no  limit  to  this  power,  in  slowly  and  beautifully 
adapting  each  form  to  the  most  complex  relations  of  life. 
The  theory  of  natural  selection,  even  if  we  look  no  far- 
ther than  this,  seems  to  be  in  the  highest  degree  prob- 
able. I  have  already  recapitulated,  as  fairly  as  I  could, 
the  opposed  difficulties  and  objections:  now  let  us  turn 
to  the  special  facts  and  arguments  in  favour  of  the  theory. 

On  the  view  that  species  are  only  strongly  marked 
and  permanent  varieties,  and  that  each  species  first 
existed  as  a  variety,  we  can  see  Avhy  it  is  that  no  line 
of  demarcation  can  be  drawn  between  species,  commonly 
supposed  to  have  been  produced  by  special  acts  of  crea- 
tion, and  varieties  which  are  acknowledged  to  have  been 
produced  by  secondary  laws.  On  this  same  view  we  can 
understand  how  it  is  that  in  a  region  where  many  species 
of  a  genus  have  been  produced,  and  where  they  now 
flourish,  these  same  species  should  present  many  varie- 
ties; for  where  the  manufactory  of  species  has  been  ac- 
tive, we  might  expect,  as  a  general  rule,  to  find  it  still  in 
action;  and  this  is  the  case  if  varieties  be  incipient  spe- 
cies. Moreover,  the  species  of  the  larger  genera,  which 
afford  the  greater  number  of  varieties  or  incipient  spe- 
cies, retain  to  a  certain  degree  the  character  of  varieties; 
for  they  differ  from  each  other  by  a  less  amount  of  differ- 
ence than  do  the  species  of  smaller  genera.  The  closely 


CHAP.  XV.]  RECAPITULATION.  281 

allied  species  also  of  the  larger  genera  apparently  have 
restricted  ranges,  and  in  their  affinities  they  are  clustered 
in  little  groups  round  other  species — in  both  respects 
resembling  varieties.  These  are  strange  relations  on 
the  view  that  each  species  was  independently  created, 
but  are  intelligible  if  each  existed  first  as  a  variety. 

As  each  species  tends  by  its  geometrical  rate  of  repro- 
duction to  increase  inordinately  in  number;  and  as  the 
modified  descendants  of  each  species  will  be  enabled  to 
increase  by  as  much  as  they  become  more  diversified  in 
habits  and  structure,  so  as  to  be  able  to  seize  on  many 
and  widely  different  places  in  the  economy  of  nature, 
there  will  be  a  constant  tendency  in  natural  selection 
to  preserve  the  most  divergent  offspring  of  any  one  spe- 
cies. Hence,  during  a  long-continued  course  of  modi- 
fication, the  slight  differences  characteristic  of  varie- 
ties of  the  same  species,  tend  to  be  augmented  into  the 
greater  differences  characteristic  of  the  species  of  the 
same  genus.  Xew  and  improved  varieties  will  inevitably 
supplant  and  exterminate  the  older,  less  improved,  and 
intermediate  varieties;  and  thus  species  are  rendered  to 
a  large  extent  defined  and  distinct  objects.  Dominant 
species  belonging  to  the  larger  groups  within  each  class 
tend  to  give  birth  to  new  and  dominant  forms;  so  that 
each  large  group  tends  to  become  still  larger,  and  at  the 
same  time  more  divergent  in  character.  But  as  all 
groups  cannot  thus  go  on  increasing  in  size,  for  the 
world  would  not  hold  them,  the  more  dominant  groups 
beat  the  less  dominant.  This  tendency  in  the  large 
groups  to  go  on  increasing  in  size  and  diverging  in  char- 
acter, together  with  the  inevitable  contingency  of  much 
extinction,  explains  the  arrangement  of  all  the  forms  of 
life  in  groups  subordinate  to  groups,  all  within  a  few 
44 


2S2  RECAPITULATION.  [CHAP.  XV. 

great  classes,  which  has  prevailed  throughout  all  time. 
This  grand  fact  of  the  grouping  of  all  organic  beings 
under  what  is  called  the  Natural  System,  is  utterly  in- 
explicable on  the  theory  of  creation. 

As  natural  selection  acts  solely  by  accumulating 
slight,  successive,  favourable  variations,  it  can  produce 
no  great  or  sudden  modifications;  it  can  act  only  by  short 
and  slow  steps.  Hence,  the  canon  of  "  Natura  non  facit 
saltum,"  which  every  fresh  addition  to  our  knowledge 
tends  to  confirm,  is  on  this  theory  intelligible.  We  can 
see  why  throughout  nature  the  same  general  end  is 
gained  by  an  almost  infinite  diversity  of  means,  for 
every  peculiarity  when  once  acquired  is  long  inherited, 
and  structures  already  modified  in  many  different  ways 
have  to  be  adapted  for  the  same  general  purpose.  We 
can,  in  short,  see  why  nature  is  prodigal  in  variety, 
though  niggard  in  innovation.  But  why  this  should  be 
a  law  of  nature  if  each  species  has  been  independently 
created  no  man  can  explain. 

Many  other  facts  are,  as  it  seems  to  me,  explicable  on 
this  theory.  Hpw  strange  it  is  that  a  bird,  under  the 
form  of  a  woodpecker,  should  prey  on  insects  on  the 
ground;  that  upland  geese  which  rarely  or  never  swim, 
should  possess  webbed  feet;  that  a  thrush-like  bird 
should  dive  and  feed  on  sub-aquatic  insects;  and  that  a 
petrel  should  have  the  habits  and  structure  fitting  it  for 
the  life  of  an  auk !  and  so  in  endless  other  cases.  But 
on  the  view  of  each  species  constantly  trying  to  increase 
in  number,  with  natural  selection  always  ready  to  adapt 
the  slowly  varying  descendants  of  each  to  any  unoccu- 
pied or  ill-occupied  place  in  nature,  these  facts  cease  to 
be  strange,  or  might  even  have  been  anticipated. 

We  can  to  a  certain  extent  understand  how  it  is  that 


CHAP.  XV.]  RECAPITULATION.  283 

there  is  so  much  beauty  throughout  nature;  for  this 
may  be  largely  attributed  to  the  agency  of  selection. 
That  beauty,  according  to  our  sense  of  it,  is  not  univer- 
sal, must  be  admitted  by  every  one  who  will  look  at  some 
venomous  snakes,  at  some  fishes,  and  at  certain  hideous 
bats  with  a  distorted  resemblance  to  the  human  face. 
Sexual  selection  has  given  the  most  brilliant  colours, 
elegant  patterns,  and  other  ornaments  to  the  males,  and 
sometimes  to  both  sexes  of  many  birds,  butterflies,  and 
other  animals.  With  birds  it  has  often  rendered  the 
voice  of  the  male  musical' to  the  female,  as  well  as  to 
our  ears.  Flowers  and  fruit  have  been  rendered  con- 
spicuous by  brilliant  colours  in  contrast  with  the  green 
foliage,  in  order  that  the  flowers  may  be  readily  seen, 
visited  and  fertilised  by  insects,  and  the  seeds  dissem- 
inated by  birds.  How  it  comes  that  certain  colours, 
sounds,  and  forms  should  give  pleasure  to  man  and  the 
lower  animals, — that  is,  how  the  sense  of  beauty  in  its 
simplest  form  was  first  acquired, — we  do  not  know  any 
more  than  how  certain  odours  and  flavours  were  first 
rendered  agreeable. 

As  natural  selection  acts  by  competition,  it  adapts 
and  improves  the  inhabitants  of  each  country  only  in 
relation  to  their  co-inhabitants;  so  that  we  need  feel  no 
surprise  at  the  species  of  any  one  country,  although  on 
the  ordinary  view  supposed  to  have  been  created  and 
specially  adapted  for  that  country,  being  beaten  and 
supplanted  by  the  naturalised  productions  from  another 
land.  Nor  ought  we  to  marvel  if  all  the  contrivances 
in  nature  be  not,  as  far  as  we  can  judge,  absolutely  per- 
fect, as  in  the  case  even  of  the  human  eye;  or  if  some 
of  them  be  abhorrent  to  our  ideas  of  fitness.  We  need 
not  marvel  at  the  sting  of  the  bee,  when  used  against 


284  RECAPITULATION.  [CHAP.  XV. 

an  enemy,  causing  the  bee's  own  death;  at  drones  be- 
ing produced  in  such  great  numbers  for  one  single  act, 
and  being  then  slaughtered  by  their  sterile  sisters;  at 
the  astonishing  waste  of  pollen  by  our  fir-trees;  at  the 
instinctive  hatred  of  the  queen-bee  for  her  own  fertile 
daughters;  at  the  ichneumonidaB  feeding  within  the  liv- 
ing bodies  of  caterpillars;  or  at  other  such  cases.  The 
wonder  indeed  is,  on  the  theory  of  natural  selection, 
that  more  cases  of  the  want  of  absolute  perfection  have 
not  been  detected. 

The  complex  and  little  known  laws  governing  the 
production  of  varieties  are  the  same,  as  far  as  we  can 
judge,  with  the  laws  which  have  governed  the  produc- 
tion of  distinct  species.  In  both  cases  physical  condi- 
tions seem  to  have  produced  some  direct  and  definite 
effect,  but  how  much  we  cannot  say.  Thus,  when  varie- 
ties enter  any  new  station,  they  occasionally  assume  some 
of  the  characters  proper  to  the  species  of  that  station. 
With  both  varieties  and  species,  use  and  disuse  seem  to 
have  produced  a  considerable  effect;  for  it  is  impossible 
to  resist  this  conclusion  when  we  look,  for  instance,  at 
the  logger-headed  duck,  which  has  wings  incapable  of 
flight,  in  nearly  the  same  condition  as  in  the  domestic 
duck;  or  when  we  look  at  the  burrowing  tucu-tucu, 
which  is  occasionally  blind,  and  then  at  certain  moles, 
which  are  habitually  blind  and  have  their  eyes  covered 
with  skin;  or  when  we  look  at  the  blind  animals  in- 
habiting the  dark  caves  of  America  and  Europe.  With 
varieties  and  species,  correlated  variation  seems  to  have 
played  an  important  part,  so  that  when  one  part  has 
been  modified  other  parts  have  been  necessarily  modi- 
fied. With  both  varieties  and  species,  reversions  to  long- 
lost  characters  occasionally  occur.  How  inexplicable  on 


CHAP.  XV.]  RECAPITULATION.  285 

the  theory  of  creation  is  the  occasional  appearance  of 
stripes  on  the  shoulders  and  legs  of  the  several  species  of 
the  horse-genus  and  of  their  hybrids!  How  simply  is 
this  fact  explained  if  we  believe  that  these  species  are  all 
descended  from  a  striped  progenitor,  in  the  same  man- 
ner as  the  several  domestic  breeds  of  the  pigeon  are  de- 
scended from  the  blue  and  barred  rock-pigeon! 

On  the  ordinary  view  of  each  species  having  been 
independently  created,  why  should  specific  characters, 
or  those  by  which  the  species  of  the  same  genus  differ 
from  each  other,  be  more  variable  than  generic  char- 
acters in  which  they  all  agree?  Why,  for  instance, 
should  the  colour  of  a  flower  be  more  likely  to  vary  in 
any  one  species  of  a  genus,  if  the  other  species  possess 
differently  coloured  flowers,  than  if  all  possessed  the 
same  coloured  flowers?  If  species  are  only  well-marked 
varieties,  of  which  the  characters  have  become  in  a  high 
degree  permanent,  we  can  understand  this  fact;  for  they 
have  already  varied  since  they  branched  off  from  a 
common  progenitor  in  certain  characters,  by  which  they 
have  come  to  be  specifically  distinct  from  each  other; 
therefore  these  same  characters  would  be  more  likely 
again  to  vary  than  the  generic  characters  which  have 
been  inherited  without  change  for  an  immense  period. 
It  is  inexplicable  on  the  theory  of  creation  why  a  part 
developed  in  a  very  unusual  manner  in  one  species  alone 
of  a  genus,  and  therefore,  as  we  may  naturally  infer, 
of  great  importance  to  that  species,  should  be  eminently 
liable  to  variation;  but,  on  our  view,  this  part  has  under- 
gone, since  the  several  species  branched  off  from  a 
common  progenitor,  an  unusual  amount  of  variability 
and  modification,  and  therefore  we  might  expect  the 
part  generally  to  be  still  variable.  But  a  part  may  be 


286  KECAPITULATION.  [CHAP.  XV. 

developed  in  the  most  unusual  manner,  like  the  wing 
of  a  bat,  and  yet  not  be  more  variable  than  any  other 
structure,  if  the  part  be  common  to  many  subordinate 
forms,  that  is,  if  it  has  been  inherited  for  a  very  long 
period;  for  in  this  case  it  will  have  been  rendered  con- 
stant by  long-continued  natural  selection. 

Glancing  at  instincts,  marvellous  as  some  are,  they 
offer  no  greater  difficulty  than  do  corporeal  structures 
on  the  theory  of  the  natural  selection  of  successive, 
slight,  but  profitable  modifications.  "We  can  thus  under- 
stand why  nature  moves  by  graduated  steps  in  endowing 
different  animals  of  the  same  class  with  their  several 
instincts.  I  have  attempted  to  show  how  much  light 
the  principle  of  gradation  throws  on  the  admirable  archi- 
tectural powers  of  the  hive-bee.  Habit  no  doubt  often 
comes  into  play  in  modifying  instincts;  but  it  certainly 
is  not  indispensable,  as  we  see  in  the  case  of  neuter  in- 
sects, which  leave  no  progeny  to  inherit  the  effects  of 
long-continued  habit.  On  the  view  of  all  the  species  of 
the  same  genus  having  descended  from  a  common  parent, 
and  having  inherited  much  in  common,  we  can  under- 
stand how  it  is  that  allied  species,  when  placed  under 
widely  different  conditions  of  life,  yet  follow  nearly  the 
same  instincts;  why  the  thrushes  of  tropical  and  tem- 
perate South  America,  for  instance,  line  their  nests  with 
mud  like  our  British  species.  On  the  view  of  instincts 
having  been  slowly  acquired  through  natural  selection, 
we  need  not  marvel  at  some  instincts  being  not  perfect 
and  liable  to  mistakes,  and  at  many  instincts  causing 
other  animals  to  suffer. 

If  species  be  only  well-marked  and  permanent  varie- 
ties, we  can  at  once  see  why  their  crossed  offspring  should 
follow  the  same  complex  laws  in  their  degrees  and  kinds 


CHAP.  XV.]  RECAPITULATION.  287 

of  resemblance  to  their  parents, — in  being  absorbed 
into  each  other  by  successive  crosses,  and  in  other  such 
points, — as  do  the  crossed  offspring  of  acknowledged 
varieties.  This  similarity  would  be  a  strange  fact,  if 
species  had  been  independently  created  and  varieties 
had  been  produced  through  secondary  laws. 

If  we  admit  that  the  geological  record  is  imperfect 
to  an  extreme  degree,  then  the  facts,  which  the  record 
does  give,  strongly  support  the  theory  of  descent  with 
modification.  New  species  have  come  on  the  stage  slow- 
ly and  at  successive  intervals;  and  the  amount  of  change, 
after  equal  intervals  of  time,  is  widely  different  in  dif- 
ferent groups.  The  extinction  of  species  and  of  whole 
groups  of  species  which  has  played  so  conspicuous  a 
part  in  the  history  of  the  organic  world,  almost  inevitably 
follows  from  the  principle  of  natural  selection;  for  old 
forms  are  supplanted  by  new  and  improved  forms. 
Neither  single  species  nor  groups  of  species  reappear 
when  the  chain  of  ordinary  generation  is  once  broken. 
The  gradual  diffusion  of  dominant  forms,  with  the  slow 
modification  of  their  descendants,  causes  the  forms  of 
life,  after  long  intervals  of  time,  to  appear  as  if  they  had 
changed  simultaneously  throughout  the  world.  The  fact 
of  the  fossil  remains  of  each  formation  being  in  some 
degree  intermediate  in  character  between  the  fossils  in 
the  formations  above  and  below,  is  simply  explained  by 
their  intermediate  position  in  the  chain  of  descent.  The 
grand  fact  that  all  extinct  beings  can  be  classed  with 
all  recent  beings,  naturally  follows  from  the  living  and 
the  extinct  being  the  offspring  of  common  parents.  As 
species  have  generally  diverged  in  character  during  their 
long  course  of  descent  and  modification,  we  can  under- 
stand why  it  is  that  the  more  ancient  forms,  or  early 


288  RECAPITULATION.  •  [CHAP.  XV. 

progenitors  of  each  group,  so  often  occupy  a  position 
in  some  degree  intermediate  between  existing  groups. 
Recent  forms  are  generally  looked  upon  as  being,  on  the 
whole,  higher  in  the  scale  of  organisation  than  ancient 
forms;  and  they  must  be  higher,  in  so  far  as  the  later 
and  more  improved  forms  have  conquered  the  older  and 
less  improved  forms  in  the  struggle  for  life;  they  have 
also  generally  had  their  organs  more  specialised  for  dif- 
ferent functions.  This  fact  is  perfectly  compatible  with 
numerous  beings  still  retaining  simple  and  but  little 
improved  structures,  fitted  for  simple  conditions  of  life; 
it  is  likewise  compatible  with  some  forms  having  retro- 
graded in  organisation,  by  having  become  at  each  stage 
of  descent  better  fitted  for  new  and  degraded  habits  of 
life.  Lastly,  the  wonderful  law  of  the  long  endurance 
of  allied  forms  on  the  same  continent, — of  marsupials 
in  Australia,  of  edentata  in  America,  and  other  such 
cases, — is  intelligible,  for  within  the  same  country  the 
existing  and  the  extinct  will  be  closely  allied  by  descent. 
Looking  to  geographical  distribution,  if  we  admit 
that  there  has  been  during  the  long  course  of  ages  much 
migration  from  one  part  of  the  world  to  another,  owing 
to  former  climatal  and  geographical  changes  and  to  the 
many  occasional  and  unknown  means  of  dispersal,  then 
we  can  understand,  on  the  theory  of  descent  with  modi- 
fication, most  of  the  great  leading  facts  in  Distribution. 
We  can  see  why  there  should  be  so  striking  a  parallelism 
in  the  distribution  of  organic  beings  throughout  space, 
and  in  their  geological  succession  throughout  time;  for 
in  both  cases  the  beings  have  been  connected  by  the 
bond  of  ordinary  generation,  and  the  means  of  modifica- 
tion have  been  the  same.  We  see  the  full  meaning  of 
the  wonderful  fact,  which  has  struck  every  traveller 


CHAP.  XV.]  RECAPITULATION.  2S9 

namely,  that  on  the  same  continent,  under  the  most 
diverse  conditions,  under  heat  and  cold,  on  mountain 
and  lowland,  on  deserts  and  marshes,  most  of  the  inhabit- 
ants within  each  great  class  are  plainly  related;  for  they 
are  the  descendants  of  the  same  progenitors  and  early 
colonists.  On  this  same  principle  of  former  migration, 
combined  in  most  cases  with  modification,  we  can  under- 
stand, by  the  aid  of  the  Glacial  period,  the  identity  of 
some  few  plants,  and  the  close  alliance  of  many  others, 
on  the  most  distant  mountains,  and  in  the  northern  and 
southern  temperate  zones;  and  likewise  the  close  alli- 
ance of  some  of  the  inhabitants  of  the  sea  in  the  north- 
ern and  southern  temperate  latitudes,  though  separated 
by  the  whole  intertropical  ocean.  Although  two  coun- 
tries may  present  physical  conditions  as  closely  similar  as 
the  same  species  ever  require,  we  need  feel  no  surprise  at 
their  inhabitants  being  widely  different,  if  they  have 
been  for  a  long  period  completely  sundered  from  each 
other;  for  as  the  relation  of  organism  to  organism  is  the 
most  important  of  all  relations,  and  as  the  two  countries 
will  have  received  colonists  at  various  periods  and  in 
different  proportions,  from  some  other  country  or  from 
each  other,  the  course  of  modification  in  the  two  areas 
will  inevitably  have  been  different. 

On  this  view  of  migration,  with  subsequent  modifica- 
tion, we  see  why  oceanic  islands  are  inhabited  by  only 
few  species,  but  of  these,  why  many  are  peculiar  or 
endemic  forms.  We  clearly  see  why  species  belonging 
to  those  groups  of  animals  which  cannot  cross  wide 
spaces  of  the  ocean,  as  frogs  and  terrestrial  mammals,  do 
not  inhabit  oceanic  islands;  and  why,  on  the  other  hand, 
new  and  peculiar  species  of  bats,  animals  which  can 
traverse  the  ocean,  are  often  found  on  islands  far  dis- 


290  RECAPITULATION.  [CHAP.  XV. 

tant  from  any  continent.  Such  cases  as  the  presence  of 
peculiar  species  of  bats  on  oceanic  islands  and  the  ab- 
sence of  all  other  terrestrial  mammals,  are  facts  utterly 
inexplicable  on  the  theory  of  independent  acts  of  crea- 
tion. 

The  existence  of  closely  allied  or  representative  spe- 
cies in  any  two  areas,  implies,  on  the  theory  of  descent 
with  modification,  that  the  same  parent-forms  formerly 
inhabited  both  areas;  and  we  almost  invariably  find  that 
wherever  many  closely  allied  species  inhabit  two  areas, 
some  identical  species  are  still  common  to  both.  Where- 
ever  many  closely  allied  yet  distinct  species  occur,  doubt- 
ful forms  and  varieties  belonging  to  the  same  groups 
likewise  occur.  It  is  a  rule  of  high  generality  that  the 
inhabitants  of  each  area  are  related  to  the  inhabitants  of 
the  nearest  source  whence  immigrants  might  have  been 
derived.  We  see  this  in  the  striking  relation  of  nearly 
all  the  plants  and  animals  of  the  Galapagos  archipelago, 
of  Juan  Fernandez,  and  of  the  other  American  islands, 
to  the  plants  and  animals  of  the  neighbouring  American 
mainland;  and  of  those  of  the  Cape  de  Verde  archi- 
pelago, and  of  the  other  African  islands  to  the  African 
mainland.  It  must  be  admitted  that  these  facts  receive 
no  explanation  on  the  theory  of  creation. 

The  fact,  as  we  have  seen,  that  all  past  and  present 
organic  beings  can  be  arranged  within  a  few  great  classes, 
in  groups  subordinate  to  groups,  and  with  the  extinct 
groups  often  falling  in  between  the  recent  groups,  is 
intelligible  on  the  theory  of  natural  selection  with  its 
contingencies  of  extinction  and  divergence  of  character. 
On  these  same  principles  we  see  how  it  is,  that  the  mu- 
tual affinities  of  the  forms  within  each  class  are  so  com- 
plex and  circuitous.  We  see  why  certain  characters 


CHAP.  XV.]  RECAPITULATION.  291 

are  far  more  serviceable  than  others  for  classification; — 
why  adaptive  characters,  though  of  paramount  import- 
ance to  the  beings,  are  of  hardly  any  importance  in 
classification;  why  characters  derived  from  rudimentary 
parts,  though  of  no  service  to  the  beings,  are  often  of 
high  classificatory  value;  and  why  embryological  char- 
acters are  often  the  most  valuable  of  all.  The  real 
affinities  of  all  organic  beings,  in  contradistinction  to 
their  adaptive  resemblances,  are  due  to  inheritance  or 
community  of  descent.  The  Natural  System  is  a  gene- 
alogical arrangement,  with  the  acquired  grades  of  dif- 
ference, marked  by  the  terms,  varieties,  species,  genera, 
families,  &c.;  and  we  have  to  discover  the  lines  of  de- 
scent by  the  most  permanent  characters  whatever  they 
may  be  and  of  however  slight  vital  importance. 

The  similar  framework  of  bones  in  the  hand  of  a 
man,  wing  of  a  bat,  fin  of  the  porpoise,  and  leg  of  the 
horse, — the  same  number  of  vertebras  forming  the  neck 
of  the  giraffe  and  of  the  elephant, — and  innumerable 
other  such  facts,  at  once  explain  themselves  on  the  theory 
of  descent  with  slow  and  slight  successive  modifications. 
The  similarity  of  pattern  in  the  wing  and  in  the  leg  of 
a  bat,  though  used  for  such  different  purpose, — in  the 
jaws  and  legs  of  a  crab, — in  the  petals,  stamens,  and  pis- 
tils of  a  flower,  is  likewise,  to  a  large  extent,  intelligible 
on  the  view  of  the  gradual  modification  of  parts  or  or- 
gans, which  were  aboriginally  alike  in  an  early  progeni- 
tor in  each  of  these  classes.  On  the  principle  of  succes- 
sive variations  not  always  supervening  at  an  early  age, 
and  being  inherited  at  a  corresponding  not  early  period 
of  life,  we  clearly  see  why  the  embryos  of  mammals, 
birds,  reptiles,  and  fishes  should  be  so  closely  similar,  and 
so  unlike  the  adult  forms.  We  may  cease  marvelling  at 


292  RECAPITULATION.  [CHAP.  XV. 

the  embryo  of  an  air-breathing  mammal  or  bird  having 
branchial  slits  and  arteries  running  in  loops,  like  those 
of  a  fish  which  has  to  breathe  the  air  dissolved  in  water 
by  the  aid  of  well-developed  branchiae. 

Disuse,  aided  sometimes  by  natural  selection,  will 
often  have  reduced  organs  when  rendered  useless  under 
changed  habits  or  conditions  of  life;  and  we  can  under- 
stand on  this  view  the  meaning  of  rudimentary  organs. 
But  disuse  and  selection  will  generally  act  on  each  crea- 
ture, when  it  has  come  to  maturity  and  has  to  play  its 
full  part  in  the  struggle  for  existence,  and  will  thus  have 
little  power  on  an  organ  during  early  life;  hence  the 
organ  will  not  be  reduced  or  rendered  rudimentary  at 
this  early  age.  The  calf,  for  instance,  has  inherited 
teeth,  which  never  cut  through  the  gums  of  the  upper 
jaw,  from  an  early  progenitor  having  well-developed 
teeth;  and  we  may  believe,  that  the  teeth  in  the  mature 
animal  were  formerly  reduced  by  disuse,  owing  to  the 
tongue  and  palate,  or  lips,  having  become  excellently 
fitted  through  natural  selection  to  browse  without  their 
aid;  whereas  in  the  calf,  the  teeth  have  been  left  un- 
affected, and  on  the  principle  of  inheritance  at  corre- 
sponding ages  have  been  inherited  from  a  remote  period 
to  the  present  day.  On  the  view  of  each  organism  with 
all  its  separate  parts  having  been  specially  created,  how 
utterly  inexplicable  is  it  that  organs  bearing  the  plain 
stamp  of  inutility,  such  as  the  teeth  in  the  embryonic 
calf  or  the  shrivelled  wings  under  the  soldered  wing- 
covers  of  many  beetles,  should  so  frequently  occur. 
Nature  may  be  said  to  have  taken  pains  to  reveal  her 
scheme  of  modification,  by  means  of  rudimentary  organs, 
of  embryological  and  homologous  structures,  but  we  are 
too  blind  to  understand  her  meaning. 


CHAP.  XV.]  CONCLUSION.  293 

I  have  now  recapitulated  the  facts  and  considerations 
which  nave  thoroughly  convinced  me  that  species  have 
been  modified,  during  a  long  course  of  descent.  This 
has  been  effected  chiefly  through  the  natural  selection 
of  numerous  successive,  slight,  favourable  variations; 
aided  in  an  important  manner  by  the  inherited  effects  of 
the  use  and  disuse  of  parts;  and  in  an  unimportant  man- 
ner, that  is  in  relation  to  adaptive  structures,  whether 
past  or  present,  by  the  direct  action  of  external  condi- 
tions, and  by  variations  which  seem  to  us  in  our  ignor- 
ance to  arise  spontaneously.  It  appears  that  I  formerly 
underrated  the  frequency  and  value  of  these  latter  forms 
of  variation,  as  leading  to  permanent  modifications  of 
structure  independently  of  natural  selection.  But  as  my 
conclusions  have  lately  been  much  misrepresented,  and 
it  has  been  stated  that  I  attribute  the  modification  of 
species  exclusively  to  natural  selection,  I  may  be  per- 
mitted to  remark  that  in  the  first  edition  of  this  work, 
and  subsequently,  I  placed  in  a  most  conspicuous  posi- 
tion— namely,  at  the  close  of  the  Introduction — the 
following  words:  "  I  am  convinced  that  natural  selection 
has  been  the  main  but  not  the  exclusive  means  of  modi- 
fication." This  has  been  of  no  avail-.  Great  is  the  power 
of  steady  misrepresentation;  but  the  history  of  science 
shows  that  fortunately  this  power  does  not  long  endure. 

It  can  hardly  be  supposed  that  a  false  theory  would 
explain,  in  so  satisfactory  a  manner  as  does  the  theory 
of  natural  selection,  the  several  large  classes  of  facts 
above  specified.  It  has  recently  been  objected  that  this 
is  an  unsafe  method  of  arguing;  but  it  is  a  method  used 
in  judging  of  the  common  events  of  life,  and  has  often 
been  used  by  the  greatest  natural  philosophers.  The 
undulatory  theory  of  light  has  thus  been  arrived  at;  and 


29±  CONCLUSION.  [CHAP.  XV. 

the  belief  in  the  revolution  of  the  earth  on  its  own  axis 
was  until  lately  supported  by  hardly  any  direct  eVidence. 
It  is  no  valid  objection  that  science  as  yet  throws  no 
light  on  the  far  higher  problem  of  the  essence  or  origin 
of  life.  Who  can  explain  what  is  the  essence  of  the 
attraction  of  gravity?  No  one  now  objects  to  following 
out  the  results  consequent  on  this  unknown  element 
of  attraction;  nowithstanding  that  Leibnitz  formerly  ac- 
cused Newton  of  introducing  "  occult  qualities  and 
miracles  into  philosophy." 

I  see  no  good  reason  why  the  views  given  in  this  vol- 
ume should  shock  the  religious  feelings  of  any  one.  It 
is  satisfactory,  as  showing  how  transient  such  impres- 
sions are,  to  remember  that  the  greatest  discovery  ever 
made  by  man,  namely,  the  law  of  the  attraction  of  grav- 
ity, was  also  attacked  by  Leibnitz,  "  as  subversive  of 
natural,  and  inferentially  of  revealed,  religion."  A  cele- 
brated author  and  divine  has  written  to  me  that  "  he  has 
."  gradually  learnt  to  see  that  it  is  just  as  noble  a  concep- 
"  tion  of  the  Deity  to  believe  that  He  created  a  few  ori- 
"  ginal  forms  capable  of  self -development  into  other  and 
"  needful  forms,  as  to  believe  that  He  required  a  fresh  act 
"  of  creation  to  supply  the  voids  caused  by  the  action  of 
"  His  laws." 

Why,  it  may  be  asked,  until  recently  did  nearly  all 
the  most  eminent  living  naturalists  and  geologists  dis- 
believe in  the  mutability  of  species.  It  cannot  be  as- 
serted that  organic  beings  in  a  state  of  nature  are  sub- 
ject to  no  variation;  it  cannot  be  proved  that  the 
amount  of  variation  in  the  course  of  long  ages  is  a  lim- 
ited quantity;  no  clear  distinction  has  been,  or  can  be, 
drawn  between  species  and  well-marked  varieties.  It 
cannot  be  maintained  that  species  when  intercrossed  are 


CIIAP.  XV.]  CONCLUSION.  295 

invariably  sterile,  and  varieties  invariably  fertile;  or 
that  sterility  is  a  special  endowment  and  sign  of  creation. 
The  belief  that  species  were  immutable  productions  was 
almost  unavoidable  as  long  as  the  history  of  the  world 
was  thought  to  be  of  short  duration;  and  now  that  we 
have  acquired  some  idea  of  the  lapse  of  time,  we  are  too 
apt  to  assume,  without  proof,  that  the  geological  record 
is  so  perfect  that  it  would  have  afforded  us  plain  evidence 
of  the  mutation  of  species,  if  they  had  undergone  mu- 
tation. 

But  the  chief  cause  of  our  natural  unwillingness  to 
admit  that  one  species  has  given  birth  to  clear  and  dis- 
tinct species,  is  that  we  are  always  slow  in  admitting 
great  changes  of  which  we  do  not  see  the  steps.  The 
difficulty  is  the  same  as  that  felt  by  so  many  geologists, 
when  Lyell  first  insisted  that  long  lines  of  inland  cliffs 
had  been  formed,  and  great  valleys  excavated,  by  the 
agencies  which  we  see  still  at  work.  The  mind  cannot 
possibly  grasp  the  full  meaning  of  the  term  of  even  a 
million  years;  it  cannot  add  up  and  perceive  the  full 
effects  of  many  slight  variations,  accumulated  during  an 
almost  infinite  number  of  generations. 

Although  I  am  fully  convinced  of  the  truth  of  the 
views  given  in  this  volume  under  the  form  of  an  abstract, 
I  by  no  means  expect  to  convince  experienced  naturalists 
whose  minds  are  stocked  with  a  multitude  of  facts  all 
viewed,  during  a  long  course  of  years,  from  a  point  of 
view  directly  opposite  to  mine.  It  is  so  easy  to  hide 
our  ignorance  under  such  expressions  as  the  "  plan  of 
creation,"  "  unity  of  design,"  &c.,  and  to  think  that  we 
give  an  explanation  when  we  only  re-state  a  fact.  Any 
one  whose  disposition  leads  him  to  attach  more  weight 
to  unexplained  difficulties  than  to  the  explanation  of  a 


296  CONCLUSION.  [CHAP.  XV. 

certain  number  of  facts  will  certainly  reject  the  theory. 
A  few  naturalists,  endowed  with  much  flexibility  of 
mind,  and  who  have  already  begun  to  doubt  the  immu- 
tability of  species,  may  be  influenced  by  this  volume; 
but  I  look  with  confidence  to  the  future, — to  young  and 
rising  naturalists,  who  will  be  able  to  view  both  sides  of 
the  question  with  impartiality.  Whoever  is  led  to  be- 
lieve that  species  are  mutable  will  do  good  service  by 
conscientiously  expressing  his  conviction;  for  thus  only 
can  the  load  of  prejudice  by  which  this  subject  is  over- 
whelmed be  removed. 

Several  eminent  naturalists  have  of  late  published 
their  belief  that  a  multitude  of  reputed  species  in  each 
genus  are  not  real  species;  but  that  other  species  are 
real,  that  is,  have  been  independently  created.  This 
seems  to  me  a  strange  conclusion  to  arrive  at.  They 
admit  that  a  multitude  of  forms,  which  till  lately  they 
themselves  thought  were  special  creations,  and  which 
are  still  thus  looked  at  by  the  majority  of  naturalists, 
and  which  consequently  have  all  the  external  character- 
istic features  of  true  species, — they  admit  that  these 
have  been  produced  by  variation,  but  they  refuse  to 
extend  the  same  view  to  other  and  slightly  different 
forms.  Nevertheless  they  do  not  pretend  that  they  can 
define,  or  even  conjecture,  which  are  the  created  forms 
of  life,  and  which  are  those  produced  by  secondary  laws. 
They  admit  variation  as  a  vcra  causa  in  one  case,  they 
arbitrarily  reject  it  in  another,  without  assigning  any 
distinction  in  the  two  cases.  The  day  will  come  when 
this  will  be  given  as  a  curious  illustration  of  the  blind- 
ness of  preconceived  opinion.  These  authors  seem  no 
more  startled  at  a  miraculous  act  of  creation  than  at  an 
ordinary  birth.  But  do  they  really  believe  that  at  innu- 


CHAP.  XV.]  CONCLUSION.  297 

merable  periods  in  the  earth's  history  certain  elemental 
atoms  have  been  commanded  suddenly  to  flash  into  liv- 
ing tissues?  Do  they  believe  that  at  each  supposed  act 
of  creation  one  individual  or  many  were  produced? 
Were  all  the  infinitely  numerous  kinds  of  animals  and 
plants  created  as  eggs  or  seed,  or  as  full  grown?  and  in 
the  case  of  mammals,  were  they  created  bearing  the 
false  marks  of  nourishment  from  the  mother's  womb? 
Undoubtedly  some  of  these  same  questions  cannot  be 
answered  by  those  who  believe  in  the  appearance  or 
creation  of  only  a  few  forms  of  life,  or  of  some  one  form 
alone.  It  has  been  maintained  by  several  authors  that 
it  is  as  easy  to  believe  in  the  creation  of  a  million  beings 
as  of  one;  but  Maupertuis'  philosophical  axiom  "  of  least 
action "  leads  the  mind  more  willingly  to  admit  the 
smaller  number;  and  certainly  we  ought  not  to  believe 
that  innumerable  beings  within  each  great  class  have 
been  created  with  plain,  but  deceptive,  marks  of  descent 
from  a  single  parent. 

As  a  record  of  a  former  state  of  things,  I  have  re- 
tained in  the  foregoing  paragraphs,  and  elsewhere,  sev- 
eral sentences  which  imply  that  naturalists  believe  in  the 
separate  creation  of  each  species;  and  I  have  been  much 
censured  for  having  thus  expressed  myself.  But  un- 
doubtedly this  was  the  general  belief  when  the  first  edi- 
tion of  the  present  work  appeared.  I  formerly  spoke 
to  very  many  naturalists  on  the  subject  of  evolution, 
and  never  once  met  with  any  sympathetic  agreement. 
It  is  probable  that  some  did  then  believe  in  evolution, 
but  they  were  either  silent,  or  expressed  themselves  so 
ambiguously  that  it  was  not  easy  to  understand  their 
meaning.  Now  things  are  wholly  changed,  and  almost 
every  naturalist  admits  the  great  principle  of  evolution. 
45 


298  CONCLUSION.  [CHAP.  XV. 

There  are,  however,  some  who  still  think  that  species 
have  suddenly  given  birth,  through  quite  unexplained 
means,  to  new  and  totally  different  forms:  but,  as  I 
have  attempted  to  show,  weighty  evidence  can  be  op- 
posed to  the  admission  of  great  and  abrupt  modifications. 
Under  a  scientific  point  of  view,  and  as  leading  to  fur- 
ther investigation,  but  little  advantage  is  gained  by  be- 
lieving that  new  forms  are  suddenly  developed -in  an  in- 
explicable manner  from  old  and  widely  different  forms, 
over  the  old  belief  in  the  creation  of  species  from  the 
dust  of  the  earth. 

It  may  be  asked  how  far  I  extend  the  doctrine  of  the 
modification  of  species.  The  question  is  difficult  to 
answer,  because  the  more  distinct  the  forms  are  which 
we  consider,  by  so  much  the  arguments  in  favour  of 
community  of  descent  become  fewer  in  number  and 
less  in  force.  But  some  arguments  of  the  greatest  weight 
extend  very  far.  All  the  members  of  whole  classes 
are  connected  together  by  a  chain  of  affinities,  and  all 
can  be  classed  on  the  same  principle,  in  groups  sub- 
ordinate to  groups.  Fossil  remains  sometimes  tend 
to  fill  up  very  wide  intervals  between  existing 
orders. 

Organs  in  a  rudimentary  condition  plainly  show  that 
an  early  progenitor  had  the  organ  in  a  fully  developed 
condition;  and  this  in  some  cases  implies  an  enormous 
amount  of  modification  in  the  descendants.  Through- 
out whole  classes  various  structures  are  formed  on  the 
same  pattern,  and  at  a  very  early  age  the  embryos  closely 
resemble  each  other.  Therefore  I  cannot  doubt  that  the 
theory  of  descent  with  modification  embraces  all  the 
members  of  the  same  great  class  or  kingdom.  I  believe 
that  animals  are  descended  from  at  most  only  four  or 


CHAP.  XV.]  CONCLUSION.  299 

five  progenitors,  and  plants  from  an  equal  or  lesser 
number. 

Analogy  would  lead  me  one  step  farther,  namely,  to 
the  belief  that  all  animals  and  plants  are  descended  from 
some  one  prototype.  But  analogy  may  be  a  deceitful 
guide.  Nevertheless  all  living  things  have  much  in 
common,  in  their  chemical  composition,  their  cellular 
structure,  their  laws  of  growth,  and  their  liability  to  in- 
jurious influences.  We  see  this  even  in  so  trifling  a 
fact  as  that  the  same  poison  often  similarly  affects  plants 
and  animals;  or  that  the  poison  secreted  by  the  gall- 
fly produces  monstrous  growths  on  the  wild  rose  or  oak- 
tree.  With  all  organic  beings,  excepting  perhaps  some 
of  the  very  lowest,  sexual  production  seems  to  be  es- 
sentially similar.  With  all,  as  far  as  is  at  present  known, 
the  germinal  vesicle  is  the  same;  so  that  all  organ- 
isms start  from  a  common  origin.  If  we  look  even  to 
the  two  main  divisions — namely,  to  the  animal  and 
vegetable  kingdoms — certain  low  forms  are  so  far  inter- 
mediate in  character  that  naturalists  have  disputed  to 
which  kingdom  they  should  be  referred.  As  Professor 
Asa  Gray  has  remarked,  "  the  spores  and  other  repro- 
"  ductive  bodies  of  many  of  the  lower  algae  may  claim 
"  to  have  first  a  characteristically  animal,  and  then  an 
"  unequivocally  vegetable  existence."  Therefore,  on  the 
principle  of  natural  selection  with  divergence  of  char- 
acter, it  does  not  seem  incredible  that,  from  some  such 
low  and  intermediate  form,  both  animals  and  plants 
may  have  been  developed;  and,  if  we  admit  this,  we 
must  likewise  admit  that  all  the  organic  beings  which 
have  ever  lived*  on  this  earth  may  be  descended  from 
some  one  primordial  form.  But  this  inference  is  chiefly 
grounded  on  analog}-,  and  it  is  immaterial  whether  or 


300  CONCLUSION.  [CHAP.  XV. 

not  it  be  accepted.  No  doubt  it  is  possible,  as  Mr.  G. 
H.  Lewes  has  urged,  that  at  the  first  commencement  of 
life  many  different  forms  were  evolved;  but  if  so,  we 
may  conclude  that  only  a  very  few  have  left  modified 
descendants.  For,  as  I  have  recently  remarked  in  regard 
to  the  members  of  each  great  kingdom,  such  as  the  Ver- 
tebrata,  Articulata,  &c.,  we  have  distinct  evidence  in 
their  embryological,  homologous,  and  rudimentary  struc- 
tures, that  within  each  kingdom  all  the  members  are 
descended  from  a  single  progenitor. 

When  the  views  advanced  by  me  in  this  volume,  and 
by  Mr.  Wallace,  or  when  analogous  views  on  the  origin 
of  species  are  generally  admitted,  we  can  dimly  foresee 
that  there  will  be  a  considerable  revolution  in  natural 
history.  Systematists  will  be  able  to  pursue  their  la- 
bours as  at  present;  but  they  will  not  be  incessantly 
haunted  by  the  shadowy  doubt  whether  this  or  that  form 
be  a  true  species.  This,  I  feel  sure  and  I  speak  after  ex- 
perience, will  be  no  slight  relief.  The  endless  disputes 
whether  or  not  some  fifty  species  of  British  brambles 
are  good  species  will  cease.  Systematists  will  have  only 
to  decide  (not  that  this  will  be  easy)  whether  any  form 
be  sufficiently  constant  and  distinct  from  other  forms, 
to  be  capable  of  definition;  and  if  definable,  whether 
the  differences  be  sufficiently  important  to  deserve  a 
specific  name.  This  latter  point  will  become  a  far  more 
essential  consideration  than  it  is  at  present;  for  differ- 
ences, however  slight,  between  any  two  forms,  if  not 
blended  by  intermediate  gradations,  are  looked  at  by 
most  naturalists  as  sufficient  to  raise  both  forms  to  the 
rank  of  species. 

Hereafter  we  shall  be  compelled  to  acknowledge  that 
the  only  distinction  between  species  and  well-marked 


CHAP.  XV.]  CONCLUSION.  301 

varieties  is,  that  the  latter  are  known,  or  believed,  to  be 
connected  at  the  present  day  by  intermediate  gradations, 
whereas  species  were  formerly  thus  connected.  Hence, 
without  rejecting  the  consideration  of  the  present  exist- 
ence of  intermediate  gradations  between  any  two  forms, 
we  shall  be  led  to  weigh  more  carefully  and  to  value 
higher  the  actual  amount  of  difference  between  them. 
It  is  quite  possible  that  forms  now  generally  acknowl- 
edged to  be  merely  varieties  may  hereafter  be  thought 
worthy  of  specific  names;  and  in  this  case  scientific  and 
common  language  will  come  into  accordance.  In  short, 
we  shall  have  to  treat  species  in  the  same  manner  as 
those  naturalists  treat  genera,  who  admit  that  genera 
are  merely  artificial  combinations  made  for  convenience. 
This  may  not  be  a  cheering  prospect;  but  we  shall  at 
least  be  free  from  the  vain  search  for  the  undiscovered 
and  undiscoverable  essence  of  the  term  species. 

The  other  and  more  general  departments  of  natural 
history  will  rise  greatly  in  interest.  The  terms  used 
by  naturalists,  of  affinity,  relationship,  community  of 
type,  paternity,  morphology,  adaptive  characters,  rudi- 
mentary and  aborted  organs,  &c.,  will  cease  to  be  meta- 
phorical, and  will  have  a  plain  signification.  When  we 
no  longer  look  at  an  organic  being  as  a  savage  looks  at 
a  ship,  as  something  wholly  beyond  his  comprehension; 
when  we  regard  every  production  of  nature  as  one  which 
has  had  a  long  history;  when  we  contemplate  every 
complex  structure  and  instinct  as  the  summing  up  of 
many  contrivances,  each  useful  to  the  possessor,  in  the 
same  way  as  any  great  mechanical  invention  is  the  sum- 
ming up  of  the  labour,  the  experience,  the  reason,  and 
even  the  blunders  of  numerous  workmen;  when  we  thus 
view  each  organic  being,  how  far  more  interesting — I 


302  CONCLUSION.  [CHAP.  XV. 

speak  from  experience — does  the  study  of  natural  history 
become ! 

A  grand  and  almost  untrodden  field  of  inquiry  will 
be  opened,  on  the  causes  and  laws  of  variation,  on  cor- 
relation, on  the  effects  of  use  and  disuse,  on  the  direct 
action  of  external  conditions,  and  so  forth.  The  study 
of  domestic  productions  will  rise  immensely  in  value. 
A  new  variety  raised  by  man  will  be  a  more  important 
and  interesting  subject  for  study  than  one  more  species 
added  to  the  infinitude  of  already  recorded  species. 
Our  classifications  will  come  to  be,  as  far  as  they  can 
be  so  made,  genealogies;  and  will  then  truly  give  what 
may  be  called  the  plan  of  creation.  The  rules  for  classi- 
fying will  no  doubt  become  simpler  when  we  have  a  defi- 
nite object  in  view.  We  possess  no  pedigrees  or  armorial 
bearings;  and  we  have  to  discover  and  trace  the  many 
diverging  lines  of  descent  in  our  natural  genealogies,  by 
characters  of  any  kind  which  have  long  been  inherited. 
Rudimentary  organs  will  speak  infallibly  with  respect 
to  the  nature  of  long-lost  structures.  Specie.s  and  groups 
of  species  which  are  called  aberrant,  and  which  may 
fancifully  be  called  living  fossils,  will  aid  us  in  form- 
ing a  picture  of  the  ancient  forms  of  life.  p]mbryology 
will  often  reveal  to  us  the  structure,  in  some  degree  ob- 
scured, of  the  prototypes  of  each  great  class. 

When  we  can  feel  assured  that  all  the  individuals 
of  the  same  species,  and  all  the  closely  allied  species 
of  most  genera,  have  within  a  not  very  remote  period 
descended  from  one  parent,  and  have  migrated  from 
some  one  birth-place;  and  when  we  better  know  the 
many  means  of  migration,  then,  by  the  light  which 
geology  now  throws,  and  will  continue  to  throw,  on 
former  changes  of  climate  and  of  the  level  of  the  land, 


CHAP.  XV.]  CONCLUSION.  393 

we  shall  surely  be  enabled  to  trace  in  an  admirable 
manner  the  former  migrations  of  the  inhabitants  of  the 
whole  world.  Even  at  present,  by  comparing  the  differ- 
ences between  the  inhabitants  of  the  sea  on  the  opposite 
sides  of  a  continent,  and  the  nature  of  the  various  in- 
habitants on  that  continent  in  relation  to  their  apparent 
means  of  immigration,  some  light  can  be  thrown  on 
ancient  geography. 

The  noble  science  of  Geology  loses  glory  from  the 
extreme  imperfection  of  the  record.  The  crust  of  the 
earth  with  its  imbedded  remains  must  not  be  looked  at 
as  a  well-filled  museum,  but  as  a  poor  collection  made  at 
hii/ard  and  at  rare  intervals.  The  accumulation  of  each 
great  fossiliferous  formation  will  be  recognised  as  having 
depended  on  an  unusual  concurrence  of  favourable  cir- 
cumstances, and  the  blank  intervals  between  the  suc- 
cessive stages  as  having  been  of  vast  duration.  But  we 
shall  be  able  to  gauge  with  some  security  the  duration 
of  these  intervals  by  a  comparison  of  the  preceding  and 
succeeding  organic  forms.  We  must  be  cautious  in  at- 
tempting to  correlate  as  strictly  contemporaneous  two 
formations,  which  do  not  include  many  identical  species, 
by  the  general  succession  of  the  forms  of  life.  As  spe- 
cies are  produced  and  exterminated  by  slowly  acting 
and  still  existing  causes,  and  not  by  miraculous  acts  of 
creation;  and  as  the  most  important  of  all  causes  of 
organic  change  is  one  which  is  almost  independent  of 
altered  and  perhaps  suddenly  altered  physical  conditions, 
namely,  the  mutual  relation  of  organism  to  organism, — 
the  improvement  of  one  organism  entailing  the  improve- 
ment or  the  extermination  of  others;  it  follows,  that  the 
amount  of  organic  change  in  the  fossils  of  consecutive 
formations  probably  serves  as  a  fair  measure  of  the 


304  CONCLUSION.  [CHAP.  XV. 

relative  though  not  actual  lapse  of  time.  A  number 
of  species,  however,  keeping  in  a  body  might  remain  for 
a  long  period  unchanged,  whilst  within  the  same  period 
several  of  these  species  by  migrating  into  new  countries 
and  coming  into  competition  with  foreign  associates, 
might  become  modified;  so  that  AVC  must  not  overrate 
the  accuracy  of  organic  change  as  a  measure  of  time. 

In  the  future  I  see  open  fields  for  far  more  important 
researches.  Psychology  will  be  securely  based  on  the 
foundation  already  well  laid  by  Mr.  Herbert  Spencer, 
that  of  the  necessary  acquirement  of  each  mental  power 
and  capacity  by  gradation.  Much  light  will  be  thrown 
on  the  origin  of  man  and  his  history. 

Authors  of  the  highest  eminence  seem  to  be  fully 
satisfied  with  the  view  that  each  species  has  been  in- 
dependently created.  To  my  mind  it  accords  better 
with  what  we  know  of  the  laws  impressed  on  matter  by 
the  Creator,  that  the  production  and  extinction  of  the 
past  and  present  inhabitants  of  the  world  should  have 
been  due  to  secondary  causes,  like  those  determining  the 
birth  and  death  of  the  individual.  When  I  view  all 
beings  not  as  special  creations,  but  as  the  lineal  descend- 
ants of  some  few  beings  which  lived  long  before  the  first 
bed  of  the  Cambrian  system  was  deposited,  they  seem 
to  me  to  become  ennobled.  Judging  from  the  past,  we 
may  safely  infer  that  not  one  living  species  will  transmit 
its  unaltered  likeness  to  a  distant  futurity.  And  of  the 
species  now  living  very  few  will  transmit  progeny  of 
any  kind  to  a  far  distant  futurity;  for  the  manner  in 
which  all  organic  beings  are  grouped,  shows  that  the 
greater  number  of  species  in  each  genus,  and  all  the 
species  in  many  genera,  have  left  no  descendants,  but 
have  become  utterly  extinct.  We  can  so  far  take  a 


CHAP.  XV.]  CONCLUSION.  305 

prophetic  glance  into  futurity  as  to  foretell  that  it  will 
be  the  common  and  widely-spread  species,  belonging  to 
the  larger  and  dominant  groups  within  each  class,  which 
will  ultimately  prevail  and  procreate  new  and  dominant 
species.  As  all  the  living  forms  of  life  are  the  lineal 
descendants  of  those  which  lived  long  before  the  Cam- 
brian epoch,  we  may  feel  certain  that  the  ordinary  suc- 
cession by  generation  has  never  once  been  broken,  and 
that  no  cataclysm  has  desolated  the  whole  world.  Hence 
we  may  look  with  some  confidence  to  a  secure  future 
of  great  length.  And  as  natural  selection  works  solely 
by  and  for  the  good  of  each  being,  all  corporeal  and 
mental  endowments  will  tend  to  progress  towards  per- 
fection. 

It  is  interesting  to  contemplate  a  tangled  bank, 
clothed  with  many  plants  of  many  kinds,  with  birds 
singing  on  the  bushes,  with  various  insects  flitting  about, 
and  with  worms  crawling  through  the  damp  earth,  and 
to  reflect  that  these  elaborately  constructed  forms,  so 
different  from  each  other,  and  dependent  upon  each 
other  in  so  complex  a  manner,  have  all  been  produced 
by  laws  acting  around  us.  These  laws,  taken  in  the 
largest  sense,  being  Growth  with  Eeproduction;  Inherit- 
ance which  is  almost  implied  by  reproduction;  Varia- 
bility from  the  indirect  and  direct  action  of  the  condi- 
tions of  life,  and  from  use  and  disuse:  a  Eatio  of  In- 
crease so  high  as  to  lead  to  a  Struggle  for  Life,  and  as 
a  consequence  to  Natural  Selection,  entailing  Divergence 
of  Character  and  the  Extinction  of  less-improved  forms. 
Thus,  from  the  war  of  nature,  from  famine  and  death, 
the  most  exalted  object  which  we  are  capable  of  con- 
ceiving, namely,  the  production  of  the  higher  animals, 
directly  follows.  There  is  grandeur  in  this  view  of  life, 


306  CONCLUSION.  [CHAP.  XV. 

with  its  several  powers,  having  been  originally  breathed 
by  the  Creator  into  a  few  forms  or  into  one;  and  that, 
whilst  this  planet  has  gone  cycling  on  according  to  the 
fixed  law  of  gravity,  from  so  simple  a  beginning  endless 
forms  most  beautiful  and  most  wonderful  have  been,  and 
are  being  evolved. 


GLOSSARY 


PRINCIPAL  SCIENTIFIC  TERMS  USED  IN  THE 
PRESENT  VOLUME.* 


ABERRANT. — Forms  or  groups  of  animals  or  plants  which  deviate 
in  important  characters  from  their  nearest  allies,  so  as  not  to 
be  easily  included  in  the  same  group  with  them,  are  said  to  be 
aberrant. 

ABERRATION  (in  Optics). — In  the  refraction  of  light  by  a  convex  lens 
the  rays  passing  through  different  parts  of  the  lens  are  brought 
to  a  focus  at  slightly  different  distances,— this  is  called  spherical 
aberration  ;  at  the  same  time  the  coloured  rays  are  separated 
by  the  prismatic  action  of  the  lens  and  likewise  brought  to  a 
focus  at  different  distances, — this  is  chromatic  aberration. 

ABNORMAL.— Contrary  to  the  general  rule. 

ABORTED.— An  organ  is  said  to  be  aborted,  when  its  development 
has  been  arrested  at  a  very  early  stage. 

ALBINISM. — Albinos  are  animals  in  which  the  usual  colouring 
matters  characteristic  of  the  species  have  not  been  produced  in 
the  skin  and  its  appendages.  Albinism  is  the  state  of  being 
an  albino. 

ALG^E. — A  class  of  plants  including  the  ordinary  sea-weeds  and  the 
filamentous  fresh-water  weeds. 


*  I  am  indebted  to  the  kindness  of  Mr.  W.  S.  Dallas  for  this 
Glossary,  which  has  been  given  because  several  readers  have  com- 
plained to  me  that  some  of  the  terms  used  were  unintelligible  to 
them.  Mr.  Dallas  has  endeavoured  to  give  the  explanations  of  the 
terms  in  as  popular  a  form  as  possible. 
807 


308  GLOSSAEY. 

ALTERNATION"  OF  GENERATIONS. — This  terra  is  applied  to  a  peculiar 
mode  of  reproduction  which  prevails  among  many  of  the  lower 
animals,  in  which  the  egg  produces  a  living  form  quite  differ- 
ent from  its  parent,  but  from  which  the  parent-form  is  repro- 
duced by  a  process  of  budding,  or  by  the  division  of  the 
substance  of  the  first  product  of  the  egg. 

AMMONITES. — A  group  of  fossil,  spiral,  chambered  shells,  allied  to 
the  existing  pearly  Nautilus,  but  having  the  partitions  be- 
tween the  chambers  waved  in  complicated  patterns  at  their 
junction  with  the  outer  wall  of  the  shell. 

ANALOGY. — That  resemblance  of  structures  which  depends  upon 
similarity  of  function,  as  in  the  wings  of  insects  and  birds. 
Such  structures  are  said  to  be  analogous,  and  to  be  analogues 
of  each  other. 

ANIMALCULE. — A  minute  animal :  generally  applied  to  those  visible 
only  by  the  microscope. 

ANNELIDS.— A  class  of  worms  in  which  the  surface  of  the  body  ex- 
hibits a  more  or  less  distinct  division  into  rings  or  segments, 
generally  provided  with  appendages  for  locomotion  and  with 
gills.  It  includes  the  ordinary  marine  worms,  the  earthworms, 
and  the  leeches. 

ANTENN.E.— Jointed  organs  appended  to  the  head  in  Insects,  Crus- 
tacea and  Centipedes,  and  not  belonging  to  the  mouth. 

ANTHERS. — The  summits  of  the  stamens  of  flowers,  in  which  the 
pollen  or  fertilising  dust  is  produced. 

APLACENTALIA,  APLACENTATA  or  Aplacental  Mammals.  See  Mam- 
malia. 

ARCHETYPAL. — Of  or  belonging  to  the  Archetype,  or  ideal  primi- 
tive form  upon  which  all  the  beings  of  a  group  seem  to  be 
organised. 

ARTICULATA.— A  great  division  of  the  Animal  Kingdom  character- 
ised generally  by  having  the  surface  of  the  body  divided  into 
rings  called  segments,  a  greater  or  less  number  of  which  are 
furnished  with  jointed  legs  (such  as  Insects,  Crustaceans  and 
Centipedes). 

ASYMMETRICAL. — Having  the  two  sides  unlike. 

ATROPHIED. — Arrested  in  development  at  a  very  early  stage. 

BALANUS. — The  genus  including  the  common  Acorn-shells  which 

live  in  abundance  on  the  rocks  of  the  sea-coast. 
BATBACHIANS. — A  class  of  animals  allied  to  the  Reptiles,  but 


GLOSSARY.  309 

undergoing  a  peculiar  metamorphosis,  in  which  the  young 
animal  is  generally  aquatic  and  breathes  by  gills.  (Examples, 
Frogs,  Toads,  and  Newts.) 

BOULDERS. — Large  transported  blocks  of  stone  generally  imbedded 
in  clays  or  gravels. 

BRACHIOPODA. — A  class  of  marine  Mollusca,  or  soft-bodied  animals, 
furnished  with  a  bivalve  shell,  attached  to  submarine  objects 
by  a  stalk  which  passes  through  an  aperture  in  one  of  the 
valves,  and  furnished  with  fringed  arms,  by  the  action  of 
which  food  is  carried  to  the  mouth. 

BRANCHLE. — Gills  or  organs  for  respiration  in  water. 

BRANCHIAL.— Pertaining  to  gills  or  branchiae. 

CAMBRIAN  SYSTEM.— A  Series  of  very  ancient  Palaeozoic  rocks, 
between  the  Laurentian  and  the  Silurian.  Until  recently 
these  were  regarded  as  the  oldest  fossiliferous  rocks. 

CANID.E.— The  Dog-family,  including  the  Dog,  Wolf,  Fox,  Jackal,  &c. 

CARAPACE. — The  shell  enveloping  the  anterior  part  of  the  body  in 
Crustaceans  generally ;  applied  also  to  the  hard  shelly  pieces 
of  the  Cirripedes. 

CARBONIFEROUS. — This  term  is  applied  to  the  great  formation 
which  includes,  among  other  rocks,  the  coal-measures.  It  be- 
longs to  the  oldest,  or  Palaeozoic,  system  of  formations. 

CAUDAL. — Of  or  belonging  to  the  tail. 

CEPHALOPODS. — The  highest  class  of  the  Mollusca,  or  soft-bodied 
animals,  characterised  by  having  the  mouth  surrounded  by  a 
greater  or  less  number  of  fleshy  arms  or  tentacles,  which,  in 
most  living  species,  are  furnished  with  sucking-cups.  (Ex- 
amples, Cuttle-fish,  Nautilus.) 

CETACEA.— An  order  of  Mammalia,  including  the  Whales,  Dolphins, 
&c.,  having  the  form  of  the  body  fish-like,  the  skin  naked,  and 
only  the  fore-limbs  developed. 

CHELONIA. — An  order  of  Reptiles  including  the  Turtles,  Tortoises, 
&c. 

CIRRIPEDES. — An  order  of  Crustaceans  including  the  Barnacles  and 
Acorn-shells.  Their  young  resemble  those  of  many  other 
Crustaceans  in  form ;  but  when  mature  they  are  always  at- 
tached to  other  objects,  either  directly  or  by  means  of  a  stalk, 
and  their  bodies  are  enclosed  by  a  calcareous  shell  composed  of 
several  pieces,  two  of  which  can  open  to  give  issue  to  a  bunch 
of  curled,  jointed  tentacles,  which  represent  the  limbs. 


310  GLOSSARY. 

Coccus.— The  genus  of  Insects  including  the  Cochineal.  In  these 
the  male  is  a  minute,  winged  fly,  and  the  female  generally  a 
motionless,  berry-like  mass. 

COCOON.— A  case  usually  of  silky  material,  in  which  insects  are 
frequently  enveloped  during  the  second  or  resting-stage  (pupa) 
of  their  existence.  The  term  "  cocoon-stage  "  is  here  used  as 
equivalent  to  "  pupa-stage." 

CCELOSPERMOUS. — A  term  applied  to  those  fruits  of  the  Umbellif- 
enu  which  have  the  seed  hollowed  on  the  inner  face. 

COLEOPTERA.— Beetles,  an  order  of  Insects,  having  a  biting  mouth 
and  the  first  pair  of  wings  more  or  less  horny,  forming  sheaths 
for  the  second  pair,  and  usually  meeting  in  a  straight  line 
down  the  middle  of  the  back. 

COLUMN.— A  peculiar  organ  in  the  flowers  of  Orchids,  in  which 
the  stamens,  style  and  stigma  (or  the  reproductive  parts)  are 
united. 

COMPOSITE  or  COMPOSITOUS  PLANTS.— Plants  in  which  the  inflores- 
cence consists  of  numerous  small  flowers  (florets)  brought  to- 
gether into  a  dense  head,  the  base  of  which  is  enclosed  by  a 
common  envelope.  (Examples,  the  Daisy,  Dandelion,  &c.) 

CONFERVA. — The  filamentous  weeds  of  fresh  water. 

CONGLOMERATE.— A  rock  made  up  of  fragments  of  rock  or  pebbles, 
cemented  together  by  some  other  material. 

COROLLA. — The  second  envelope  of  a  flower  usually  composed  of 
coloured,  leaf-like  organs  (petals),  which  may  be  united  by 
their  edges  either  in  the  basal  part  or  throughout. 

CORRELATION. — The  normal  coincidence  of  one  phenomenon,  char- 
acter, &c.,  with  another. 

CORYMB.— A  bunch  of  flowers  in  which  those  springing  from  the 
lower  part  of  the  flower  stalk  are  supported  on  long  stalks  so 
as  to  be  nearly  on  a  level  with  the  upper  ones. 

COTYLEDONS.— The  first  or  seed-leaves  of  plants. 

CRUSTACEANS. — A  class  of  articulated  animals,  having  the  skin  of 
the  body  generally  more  or  less  hardened  by  the  deposition  of 
calcareous  matter,  breathing  by  means  of  gills.  (Examples, 
Crab,  Lobster,  Shrimp,  &c.) 

CURCULIO.— The  old  generic  term  for  the  Beetles  known  as  Wee- 
vils, characterised  by  their  four-jointed  feet,  and  by  the  head 
being  produced  into  a  sort  of  beak,  upon  the  sides  of  which 
the  antennae  are  inserted. 

CUTANEOUS.— Of  or  belonging  to  the  skin. 


GLOSSARY.  3H 

DEGRADATION.— The  wearing  down  of  land  by  the  action  of  the  sea 
or  of  meteoric  agencies. 

DENUDATION.— The  wearing  away  of  the  surface  of  the  land  by 
water. 

DEVONIAN  SYSTEM  or  formation. — A  series  of  Palaeozoic  rocks,  in- 
cluding the  Old  Red  Sandstone. 

DICOTYLEDONS  or  DICOTYLEDONOUS  PLANTS. — A  class  of  plants 
characterised  by  having  two  seed-leaves,  by  the  formation  of 
new  woodt  between  the  bark  and  the  old  wood  (exogenous 
growth)  and  by  the  reticulation  of  the  veins  of  the  leaves. 
The  parts  of  the  flowers  are  generally  in  multiples  of  five. 

DIFFERENTIATION. — The  separation  or  discrimination  of  parts  or 
organs  which  in  simpler  forms  of  life  are  more  or  less 
united. 

DIMORPHIC.— Having  two  distinct  forms.— Dimorphism  is  the  con- 
dition of  the  appearance  of  the  same  species  under  two  dis- 
similar forms. 

DICECIOUS. — Having  the  organs  of  the  sexes  upon  distinct  indi- 
viduals. 

DIORITE. — A  peculiar  form  of  Greenstone. 

DORSAL.— Of  or  belonging  to  the  back. 

EDENTATA.— A  peculiar  order  of  Quadrupeds,  characterised  by  the 

absence  of  at  least  the  middle  incisor  (front)  teeth  in  both 

jaws.    (Examples,  the  Sloths  and  Armadillos.) 
ELYTRA. — The  hardened  fore-wings  of  Beetles,  serving  as  sheaths 

for  the  membranous  hind-wings,  which  constitute  the  true 

organs  of  flight. 
EMBRYO. — The  young  animal  undergoing  development  within  the 

egc  or  womb. 

EMBRYOLOGY. — The  study  of  the  development  of  the  embryo. 
ENDEMIC.— Peculiar  to  a  given  locality. 
ENTOMOSTRACA. — A  division  of  the  class  Crustacea,  having  all  the 

segments  of  the  body  usually  distinct,  gills  attached  to  the 

feet  or  organs  of  the  mouth,  and  the  feet  fringed  with  fine 

hairs.     They  are  generally  of  small  size. 
EOCENE.— The  earliest  of  the  three  divisions  of  the  Tertiary  epoch 

of  geologists.    Rocks  of  this  age  contain  a  small  proportion  of 

shells  identical  with  species  now  living. 
EPIIEMEROUS  INSECTS. — Insects  allied  to  the  May-fly. 


312  GLOSSARY. 

FAUNA. — The  totality  of  the  animals  naturally  inhabiting  a  cer- 
tain country  or  region,  or  which  have  lived  during  a  given 
geological  period. 

FELID^:.— The  Cat-family. 

FERAL.— Having  become  wild  from  a  state  of  cultivation  or  domes- 
tication. 

FLORA.— The  totality  of  the  plants  growing  naturally  in  a  country, 
or  during  a  given  geological  period. 

FLORETS.— Flowers  imperfectly  developed  in  some  respects,  and 
collected  into  a  dense  spike  or  head,  as  in  the  Grasses,  the 
Dandelion,  &c. 

FffiTAL. — Of  or  belonging  to  the  foetus,  or  embryo  in  course  of  de- 
velopment. 

FORAMINIFERA. — A  class  of  animals  of  very  low  organisation,  and 
generally  of  small  size,  having  a  jelly-like  body,  from  the  sur- 
face of  which  delicate  filaments  can  be  given  off  and  retracted 
for  the  prehension  of  external  objects,  and  having  a  calcareous 
or  sandy  shell,  usually  divided  into  chambers,  and  perforated 
with  small  apertures. 

FOSSILIFEROUS.— Containing  fossils. 

FOSSORIAL. — Having  a  faculty  of  digging.  The  Fossorial  Hymen- 
optera  are  a  group  of  Wasp-like  Insects,  which  burrow  in 
sandy  soil  to  make  nests  for  their  young. 

FRENUM  (pi.  FRENA). — A  small  band  or  fold  of  skin. 

FUNGI  (sing.  FUNGUS). — A  class  of  cellular  plants,  of  which  Mush- 
rooms, Toadstools,  and  Moulds,  are  familiar  examples. 

FURCULA.— The  forked  bone  formed  by  the  union  of  the  collar- 
bones in  many  birds,  such  as  the  common  Fowl. 

GALLINACEOUS  BIRDS. — An  order  of  Birds  of  which  the  common 
Fowl,  Turkey,  and  Pheasant,  are  well-known  examples. 

GALLUS.— The  genus  of  birds  which  includes  the  common  Fowl. 

GANGLION.— A  swelling  or  knot  from  which  nerves  are  given  off  as 
from  a  centre. 

GANOID  FISHES.— Fishes  covered  with  peculiar  enamelled  bony 
scales.  Most  of  them  are  extinct. 

GERMINAL  VESICLE. — A  minute  vesicle  in  the  eggs  of  animals,  from 
which  development  of  the  embryo  proceeds. 

GLACIAL  PERIOD. — A  period  of  great  cold  and  of  enormous  exten- 
sion of  ice  upon  the  surface  of  the  earth.  It  is  believed  that 
glacial  periods  have  occurred  repeatedly  during  the  geological 


GLOSSARY.  313 

history  of  the  earth,  but  the  term  is  generally  applied  to  the 
close  of  the  Tertiary  epoch,  when  nearly  the  whole  of  Europe 
was  subjected  to  an  arctic  climate. 

GLAND.— An  organ  which  secretes  or  separates  some  peculiar  prod- 
uct from  the  blood  or  sap  of  animals  or  plants. 

GLOTTIS. — The  opening  of  the  windpipe  into  the  oesophagus  or 
gullet. 

GNEISS. — A  rock  approaching  granite  in  composition,  but  more  or 
less  laminated,  and  really  produced  by  the  alteration  of  a  sedi- 
mentary deposit  after  its  consolidation. 

GRALLATORES.— The  so-called  Wading-birds  (Storks,  Cranes,  Snipes, 
&c.),  which  are  generally  furnished  with  long  legs,  bare  of 
feathers  above  the  heel,  and  have  no  membranes  between  the 
toes. 

GRANITE. — A  rock  consisting  essentially  of  crystals  of  felspar  and 
mica  in  a  mass  of  quartz. 

HABITAT.— The  locality  in  which  a  plant  or  animal  naturally  lives. 

HEMIPTERA. — An  order  or  sub-order  of  Insects,  characterised  by 
the  possession  of  a  jointed  beak  or  rostrum,  and  by  having  the 
fore-wings  horny  in  the  basal  portion  and  membranous  at  the 
extremity,  where  they  cross  each  other.  This  group  includes 
the  various  species  of  Bugs. 

HERMAPHRODITE. — Possessing  the  organs  of  both  sexes. 

HOMOLOGY.— That  relation  between  parts  which  results  from  their 
development  from  corresponding  embryonic  parts,  either  in 
different  animals,  as  in  the  case  of  the  arm  of  man,  the  fore- 

,  leg  of  a  quadruped,  and  the  wing  of  a  bird  ;  or  in  the  same  in- 
dividual, as  in  the  case  of  the  fore  and  hind  legs  in  quadrupeds, 
and  the  segments  or  rings  and  their  appendages  of  which  the 
body  of  a  worm,  a  centipede,  &c.,  is  composed.  The  latter  is 
called  serial  homology.  The  parts  which  stand  in  such  a  rela- 
tion to  each  other  are  said  to  be  homologous,  and  one  such  part 
or  organ  is  called  the  homologue  of  the  other.  In  different 
plants  the  parts  of  the  flower  are  homologous,  and  in  general 
these  parts  are  regarded  as  homologous  with  leaves. 

HOMOPTERA. — An  order  or  sub-order  of  Insects  having  (like  the 
Hemiptera)  a  jointed  beak,  but  in  which  the  fore-wings  are 
either  wholly  membranous  or  wholly  leathery.  The  Cicada, 
Frog-hoppers,  and  Aphid*-*,  arc  well-known  examples. 

HYBRID.— The  offspring  of  the  union  of  two  distinct  species. 
40 


314:  GLOSSARY. 

HYMENOPTERA.— An  order  of  insects  possessing  biting  jaws  and 
usually  four  membranous  wings  in  which  there  are  a  few  veins. 
Bees  and  Wasps  are  familiar  examples  of  this  group. 

HYPEETBOPHIED.— Excessively  developed. 

ICHNEUMONID^E. — A  family  of  Hymenopterous  insects,  the  mem- 
bers of  which  lay  their  eggs  in  the  bodies  or  eggs  of  other 
insects. 

IMAGO. — The  perfect  (generally  winged)  reproductive  state  of  an 
insect. 

INDIGENS. — The  aboriginal  animal  or  vegetable  inhabitants  of  a 
country  or  region. 

INFLORESCENCE. — The  mode  of  arrangement  of  the  flowers  of  plants. 

INFUSORIA. — A  class  of  microscopic  Animalcules,  so  called  from 
their  having  originally  been  observed  in  infusions  of  vegetable 
matters.  They  consist  of  a  gelatinous  material  enclosed  in  a 
delicate  membrane,  the  whole  or  part  of  which  is  furnished 
with  short  vibrating  hairs  (called  cilia),  by  means  of  which  the 
animalcules  swim  through  the  water  or  convey  the  minute  par- 
ticles of  their  food  to  the  orifice  of  the  mouth. 

INSECTIVOROUS.— Feeding  on  Insects. 

INVERTEBRATA,  or  INVERTEBRATE  ANIMALS. — Those  animals  which 
do  not  possess  a  backbone  or  spinal  column. 

LACUNA.— Spaces  left  among  the  tissues  in  some  of  the  lower  ani- 
mals, and  serving  in  place  of  vessels  for  the  circulation  of  the 
fluids  of  the  body. 

LAMELLATED. — Furnished  with  lamella}  or  little  plates. 

LARVA  (pi.  LARVAE). — The  first  condition  of  an  insect  at  its  issuing 
from  the  egg,  when  it  is  usually  in  the  form  of  a  grub,  cater- 
pillar, or  maggot. 

LARYNX. — The  upper  part  of  the  windpipe  opening  into  the  gullet. 

LAURENTIAN. — A  group  of  greatly  altered  and  very  ancient  rocks, 
which  is  greatly  developed  along  the  course  of  the  St.  Lau- 
rence, whence  the  name.  It  is  in  these  that  the  earliest  known 
traces  of  organic  bodies  have  been  found. 

LEGUMINOS^. — An  order  of  plants  represented  by  the  common  Peas 
and  Beans,  having  an  irregular  flower  in  which  one  petal  stands 
up  like  a  wing,  and  the  stamens  and  pistil  are  enclosed  in  a 
pheath  formed  by  two  other  petals.  The  fruit  is  a  pod  (or 
legume). 


GLOSSARY.  315 

LEMUIUD^K— A  group  of  four-handed  animals,  distinct  from  the 
Monkeys  and  approaching  the  Insectivorous  Quadrupeds  in 
some  of  their  characters  and  habits.  Its  members  have  the 
nostrils  curved  or  twisted,  and  a  claw  instead  oi'  a  nail  upon 
the  first  finger  of  the  hind  hands.. 

LEPIDOPTERA. — An  order  of  Insects,  characterised  by  the  posses- 
sion of  a  spiral  proboscis,  and  of  four  large  more  or  less 
scaly  wings.  It  includes  the  well-known  Butterflies  and 
Moths. 

LITTORAL. — Inhabiting  the  seashore. 

LOESS. — A  marly  deposit  of  recent  (Post-Tertiary)  date,  which 
occupies  a  great  part  of  the  valley  of  the  Rhine. 

MALACOSTRACA. — The  higher  division  of  the  Crustacea,  including 
the  ordinary  Crabs,  Lobsters,  Shrimps,  &c.,  together  with  the 
Woodlice  and  Sand-hoppers. 

MAMMALIA. — The  highest  class  of  animals,  including  the  ordinary 
hairy  quadrupeds,  the  Whales,  and  Man,  and  characterised  by 
the  production  of  living  young  which  are  nourished  after  birth 
by  milk  from  the  teats  (Mammce,  Mammary  glands)  of  the 
mother.  A  striking  difference  in  embryonic  development  has 
led  to  the  division  of  this  class  into  two  great  groups ;  in  one 
of  these,  when  the  embryo  has  attained  a  certain  stage,  a  vas- 
cular connection,  called  the  placenta,  is  formed  between  the 
embryo  and  the  mother ;  in  the  other  this  is  wanting,  and  the 
young  are  produced  in  a  very  incomplete  state.  The  former, 
including  the  greater  part  of  the  class,  are  called  Placental 
mammals;  the  latter,  or  Aplacental  mammals,  include  the 
Marsupials  and  Monotremes  (Ornithorhynchus). 

MAMMIFEROUS.     Having  mamma?  or  teats  (see  MAMMALIA). 

MANDIBLES,  in  Insects.— The  first  or  uppermost  pair  of  jaws,  which 
are  generally  solid,  horny,  biting  organs.  In  Birds  the  term  is 
applied  to  both  jaws  with  their  horny  coverings.  In  Quadru- 
peds the  mandible  is  properly  the  lower  jaw. 

MARSUPIALS. — An  order  of  Mammalia  in  which  the  young  are  born 
in  a  very  incomplete  state  of  development,  and  carried  by  the 
mother,  while  sucking,  in  a  ventral  pouch  (marsupium),  such 
as  the  Kangaroos,  Opossums,  &c.  (see  MAMMALIA). 

MAXILLA,  in  Insects.— -The  second  or  lower  pair  of  jaws,  which  are 
composed  of  several  joints  and  furnished  with  peculiar  jointed 
appendages  called  palpi,  or  feelers. 


316  GLOSSAKY. 

MELANISM.— The  opposite  of  albinism ;  an  undue  development  of 
colouring  material  in  the  skin  and  its  appendages. 

METAMOBPHIC  ROCKS. — Sedimentary  rocks  which  have  undergone 
alteration,  generally  by  the  action  of  heat,  subsequently  to 
their  deposition  and  consolidation. 

MOLLUSCA. — One  of  the  great  divisions  of  the  Animal  Kingdom, 
including  those  animals  which  have  a  soft  body,  usually 
furnished  with  a  shell,  and  in  which  the  nervous  ganglia,  or 
centres,  present  no  definite  general  arrangement.  They  are 
generally  known  under  the  denomination  of  "  shell-fish ; "  the 
cuttle-fish,  and  the  common  snails,  whelks,  oysters,  mussels, 
and  cockles,  may  serve  as  examples  of  them. 

MONOCOTYLEDONS,  or  MONOCOTYLEDONOUS  PLANTS.  —  Plants  in 
which  the  seed  sends  up  only  a  single  seed-leaf  (or  cotyledon) ; 
characterised  by  the  absence  of  consecutive  layers  of  wood  in 
the  stem  (endogenous  growth),  by  the  veins  of  the  leaves  being 
generally  straight,  and  by  the  parts  of  the  flowers  being  gener- 
ally in  multiples  of  three.  (Examples,  Grasses,  Lilies,  Orchids, 
Palms,  &c.) 

MORAINES. — The  accumulations  of  fragments  of  rock  brought  down 
by  glaciers. 

MORPHOLOGY. — The  law  of  form  or  structure  independent  of 
function. 

MYSIS-STAGE. — A  stage  in  the  development  of  certain  Crustaceans 
(Prawns),  in  which  they  closely  resemble  the  adults  of  a  genus 
(JUysis)  belonging  to  a  slightly  lower  group. 

NASCENT. — Commencing  development. 

NATATORY. — Adapted  for  the  purpose  of  swimming. 

NAUPLIUS-FORM. — The  earliest  stage  in  the  development  of  many 
Crustacea,  especially  belonging  to  the  lower  groups.  In  this 
stage  the  animal  has  a  short  body,  with  indistinct  indications 
of  a  division  into  segments,  and  three  pairs  of  fringed  limbs. 
This  form  of  the  common  fresh-water  Cyclops  was  described 
as  a  distinct  genus  under  the  name  of  Nauplius. 

NEURATION. — The  arrangement  of  the  veins  or  nervures  in  the 
wings  of  Insects. 

NEUTERS. — Imperfectly  developed  females  of  certain  social  insects 
(such  as  Ants  and  Bees),  which  perform  all  the  labours  of  the 
community.  Hence  they  are  also  called  workers. 

NICTITATING   MEMBRANE. — A  semi-transparent  membrane,  which 


GLOSSARY.  317 

can  be  drawn  across  the  eye  in  Birds  and  Reptiles,  either  to 
moderate  the  effects  of  a  strong  light  or  to  sweep  particles  of 
dust,  &c.,  from  the  surface  of  the  eye. 

OCELLI. — The  simple  eyes  or  stemmata  of  Insects,  usually  situated 
on  the  crown  of  the  head  between  the  great  compound  eyes. 

(ESOPHAGUS.— The  gullet. 

OOLITIC.— A  great  series  of  secondary  rocks,  so  called  from  the 
texture  of  some  of  its  members,  which  appear  to  be  made  up 
of  a  mass  of  small  egg-like  calcareous  bodies. 

OPERCULUM.— A  calcareous  plate  employed  by  many  Mollusca  to 
close  the  aperture  of  their  shell.  The  opercular  valves  of  Cir- 
ripedes  are  those  which  close  the  aperture  of  the  shell. 

ORBIT.— The  bony  cavity  for  the  reception  of  the  eye. 

ORGANISM.— An  organised  being,  whether  plant  or  animal. 

ORTHOSPERMOUS. — A  term  applied  to  those  fruits  of  the  Umbel- 
liferae  which  have  the  seed  straight. 

OSCULANT.— Forms  or  groups  apparently  intermediate  between  and 
connecting  other  groups  are  said  to  be  osculant. 

OVA.— Eggs. 

OVARIUM  or  OVARY  (in  plants).— The  lower  part  of  the  pistil  or 
female  organ  of  the  flower,  containing  the  ovules  or  incipient 
seeds ;  by  growth  after  the  other  organs  of  the  flower  have 
fallen,  it  usually  becomes  converted  into  the  fruit. 

OVIGEROUS.— Egg-bearing. 

OVULES  (of  plants).— The  seeds  in  the  earliest  condition. 

PACHYDERMS. — A  group  of  Mammalia,  so  called  from  their  thick 
skins,  and  including  the  Elephant,  Rhinoceros,  Hippopotamus, 
&c. 

PALAEOZOIC. — The  oldest  system  of  fossiliferous  rocks. 

PALPI. — Jointed  appendages  to  some  of  the  organs  of  the  mouth  in 
Insects  and  Crustacea. 

PAPILIONACE^:.— An  order  of  Plants  (see  LEGUMINOS^;).— The 
flowers  of  these  plants  are  called  papilionaceous,  or  butterfly- 
like,  from  the  fancied  resemblance  of  the  expanded  superior 
petals  to  the  wings  of  a  butterfly. 

PARASITE.— An  animal  or  plant  living  upon  or  in,  and  at  the  ex- 
pense of,  another  organism. 

PARTHENOGENESIS.— The  production  of  living  organisms  from  un- 
impregnated  eggs  or  seeds. 


318  GLOSSARY. 

PEDUNCULATED. — Supported  upon  a  stem  or  stalk.  The  peduncu- 
lated  oak  has  its  acorns  borne  upon  a  footstool. 

PELORIA  or  PELORISM. — The  appearance  of  regularity  of  structure 
in  the  flowers  of  plants  which  normally  bear  irregular  flowers. 

PELVIS.— The  bony  arch  to  which  the  hind  limbs  of  vertebrate 
animals  are  articulated. 

PETALS. — The  leaves  of  the  corolla,  or  second  circle  of  organs  in 
a  flower.  They  are  usually  of  delicate  texture  and  brightly 
coloured. 

PHYLLODINEOUS.— Having  flattened,  leaf-like  twigs  or  leafstalks 
instead  of  true  leaves. 

PIGMENT.— The  colouring  material  produced  generally  in  the  super- 
ficial parts  of  animals.  The  cells  secreting  it  are  called  pig- 
ment-cells, 

PINNATE.— Bearing  leaflets  on  each  side  of  a  central  stalk. 

PISTILS. — The  female  organs  of  a  flower,  which  occupy  a  position 
in  the  centre  of  the  other  floral  organs.  The  pistil  is  generally 
divisible  into  the  ovary  or  germen,  the  style  and  the  stigma. 

PLACENTALIA,  PLACENTATA,  or  Placental  Mammals.— See  MAM- 
MALIA. 

PLANTIGRADES. — Quadrupeds  which  walk  upon  the  whole  sole  of 
the  foot,  like  the  Bears. 

PLASTIC. — Readily  capable  of  change. 

PLEISTOCENE  PERIOD. — The  latest  portion  of  the  Tertiary  epoch. 

PLUMULE  (in  plants).— The  minute  bud  between  the  seed-leaves  of 
newly-germinated  plants. 

PLUTONIC  ROCKS. — Rocks  supposed  to  have  been  produced  by  igne- 
ous action  in  the  depths  of  the  earth. 

POLLEN.— The  male  element  in  flowering  plants;  usually  a  fine 
dust  produced  by  the  anthers,  which,  by  contact  with  the 
stigma  effects  the  fecundation  of  the  seeds.  This  impregnation 
is  brought  about  by  means  of  tubes  (pollen-tubes)  which  issue 
from  the  pollen-grains  adhering  to  the  stigma,  and  penetrate 
through  the  tissues  until  they  reach  the  ovary. 

POLTANDROUS  (flowers).— Flowers  having  many  stamens. 

POLYGAMOUS  PLANTS. — Plants  in  which  some  flowers  are  unisexual 
and  others  hermaphrodite.  The  unisexual  (male  and  female) 
flowers,  may  be  on  the  same  or  on  different  plants. 

POLYMORPHIC.— Presenting  many  forms. 

POLYZOARY. — The  common  structure  formed  by  the  cells  of  the 
Polyzoa,  such  as  the  well-known  Sea-mats. 


GLOSSARY.  319 

PREHENSILE. — Capable  of  grasping. 

PREPOTENT. — Having  a  superiority  of  power. 

PRIMARIES.— The  feathers  forming  the  tip  of  the  wing  of  a  bird, 
and  inserted  upon  that  part  which  represents  the  hand  of 
man. 

PROCESSES. — Projecting  portions  of  bones,  usually  for  the  attach- 
ment of  muscles,  ligaments,  &c. 

PROPOLIS. — A  resinous  material  collected  by  the  Hive-Bees  from 
the  opening  buds  of  various  trees. 

PROTEAN. — Exceedingly  variable. 

PROTOZOA.— The  lowest  great  division  of  the  Animal  Kingdom. 
These  animals  are  composed  of  a  gelatinous  material,  and 
show  scarcely  any  trace  of  distinct  organs.  The  Infusoria, 
Foraminifera,  and  Sponges,  with  some  other  forms,  belong  to 
this  division. 

PUPA  (pi.  PUP^E). — The  second  stage  in  the  development  of  an 
Insect,  from  which  it  emerges  in  the  perfect  (winged)  repro- 
ductive form.  In  most  insects  the  pupal  stage  is  passed  in 
perfect  repose.  The  chrysalis  is  the  pupal  state  of  butterflies. 

RADICLE.— The  minute  root  of  an  embryo  plant. 

RAMUS. — One  half  of  the  lower  jaw  in  the  Mammalia.  The  portion 
which  rises  to  articulate  with  the  skull  is  called  the  ascending 
ramus. 

RANGE.— The  extent  of  country  over  which  a  plant  or  animal  is 
naturally  spread.  Range  in  time  expresses  the  distribution  of 
a  species  or  group  through  the  fossiliferous  beds  of  the  earth's 
crust. 

RETINA.— The  delicate  inner  coat  of  the  eye,  formed  by  nervous 
filaments  spreading  from  the  optic  nerve,  and  serving  for  the 
perception  of  the  impressions  produced  by  light. 

RETROGRESSION.— Backward  development.  When  an  animal,  as  it 
approaches  maturity,  becomes  less  perfectly  organised  than 
might  be  expected  from  its  early  stages  and  known  relation- 
ships, it  is  said  to  undergo  a  retrograde  development  or  meta- 
morphosis. 

RHIZOPODS. — A  class  of  lowly  organised  animals  (Protozoa),  having 
a  gelatinous  body,  the  surface  of  which  can  be  protruded  in 
the  form  of  root-like  processes  or  filaments,  which  serve  for 
locomotion  and  the  prehension  of  food.  The  most  important 
order  is  that  of  the  Forarainifera. 


320  GLOSSARY. 

RODENTS.— The  gnawing  Mammalia,  such  as  the  Eats,  Rabbits, 
and  Squirrels.  They  are  especially  characterised  by  the  pos- 
session of  a  single  pair  of  chisel-like  cutting  teeth  in  each 
jaw,  between  which  and  the  grinding  teeth  there  is  a  great 

gap- 

RUBUS.— The  Bramble  Genus. 

RUDIMENTARY.— Very  imperfectly  developed. 

RUMINANTS. — The  group  of  Quadrupeds  which  ruminate  or  chew 
the  cud,  such  as  oxen,  sheep,  and  deer.  They  have  divided 
hoofs,  and  are  destitute  of  front  teeth  in  the  upper  jaw. 

SACRAL. — Belonging  to  the  sacrum,  or  the  bone  composed  usually 
of  two  or  more  united  vertebrae  to  which  the  sides  of  the  pelvis 
in  vertebrate  animals  are  attached. 

SARCODE. — The  gelatinous  material  of  which  the  bodies  of  the 
lowest  animals  (Protozoa)  are  composed. 

SCUTELL^E. — The  horny  plates  with  which  the  feet  of  birds  are  gen- 
erally more  or  less  covered,  especially  in  front. 

SEDIMENTARY  FORMATIONS. — Rocks  deposited  as  sediments  from 
water. 

SEGMENTS. — The  transverse  rings  of  which  the  body  of  an  articulate 
animal  or  Annelid  is  composed. 

SEPALS. — The  leaves  or  segments  of  the  calyx,  or  outermost  enve- 
lope of  an  ordinary  flower.  They  are  usually  green,  but  some- 
times brightly  coloured. 

SERRATURES. — Teeth  like  those  of  a  saw. 

SESSILE. — Not  supported  on  a  stem  or  footstalk. 

SILURIAN  SYSTEM.— A  very  ancient  system  of  fossiliferous  rocks 
belonging  to  the  earlier  part  of  the  Palaeozoic  series. 

SPECIALISATION. — The  setting  apart  of  a  particular  organ  for  the 
performance  of  a  particular  function. 

SPINAL  CHORD.— The  central  portion  of  the  nervous  system  in  the 
Vertebrata,  which  descends  from  the  brain  through  the  arches 
of  the  vertebral,  and  gives  off  nearly  all  the  nerves  to  the  va- 
rious organs  of  the  body. 

STAMENS. — The  male  organs  of  flowering  plants,  standing  in  a  circle 
within  the  petals.  They  usually  consist  of  a  filament  and  an 
anther,  the  anther  being  the  essential  part  in  which  the  pollen, 
or  fecundating  dust,  is  formed. 

STERNUM.— The  brea'st-bone. 

STIGMA.— The  apical  portion  of  the  pistil  in  flowering  plants. 


GLOSSARY.  321 

STIPULES.— Small  leafy  organs  placed  at  the  base  of  the  footstalks 

of  the  leaves  in  many  plants. 
STYLE. — The  middle  portion  of  the  perfect  pistil,  which  rises  like 

a  column  from  the  ovary  and  supports  the  stigma  at  its 

summit. 

SUBCUTANEOUS.— Situated  beneath  the  skin. 
SUCTORIAL. — Adapted  for  sucking. 
SUTURES  (in  the  skull).— The  lines  of  junction  of  the  bones  of  which 

the  skull  is  composed. 

TARSUS  (pi.  TARSI).— The  jointed  feet  of  articulate  animals,  such 

as  Insects. 
TELEOSTEAN  FISHES.— Fishes  of  the  kind  familiar  to  us  in  the 

present  day,  having  the  skeleton  usually  completely  ossified 

and  the  scales  horny. 
TENTACULA  or  TENTACLES.— Delicate  fleshy  organs  of  prehension 

or  touch  possessed  by  many  of  the  lower  animals. 
TERTIARY. — The  latest  geological  epoch,  immediately  preceding 

the  establishment  of  the  present  order  of  things. 
TRACHEA.— The  windpipe  or  passage  for  the  admission  of  air  to 

the  lungs. 
TRIDACTYLE. — Three-fingered,  or  composed  of  three  movable  parts 

attached  to  a  common  base. 
TRILOBITES. — A  peculiar  group  of  extinct  Crustaceans,  somewhat 

resembling  the  Woodlice  in  external  form,  and,  like  some  of 

them,  capable  of  rolling  themselves  up  into  a  ball.    Their 

remains  are  found  only  in  the  Palaeozoic  rocks,  and  most 

abundantly  in  those  of  Silurian  age. 
TRIMORPIIIC. — Presenting  three  distinct  forms. 

UMBELLIFER^E. — An  order  of  plants  in  which  the  flowers,  which 
contain  five  stamens  and  a  pistil  with  two  styles,  are  supported 
upon  footstalks  which  spring  from  the  top  of  the  flower  stem 
and  spread  out  like  the  wires  of  an  umbrella,  so  as  to  bring  all 
the  flowers  in  the  same  head  (umbel)  nearly  to  the  same  level. 
(Examples,  Parsley  and  Carrot). 

UNGULATA. — Hoofed  quadrupeds. 

UNICELLULAR. — Consisting  of  a  single  cell. 

VASCULAR. — Containing  blood-vessels. 
VERMIFORM. — Like  a  worm. 


322  GLOSSARY. 

VERTEBRATA:  or  VERTEBRATE  ANIMALS.— The  highest  division  of 
the  animal  kingdom,  so  called  from  the  presence  in  most 
cases  of  a  backbone  composed  of  numerous  joints  or  vertebrae, 
which  constitutes  the  centre  of  the  skeleton  and  at  the  same 
time  supports  and  protects  the  central  parts  of  the  nervous 
system. 

WHORLS.— The  circles  or  spiral  lines  in  which  the  parts  of  plants 

are  arranged  upon  the  axis  of  growth. 
WORKERS. — See  neuters. 

ZofiA-STAOE. — The  earliest  stage  in  the  development  of  many  of 
the  higher  Crustacea,  so  called  from  the  name  of  Zoea  applied 
to  these  young  animals  when  they  were  supposed  to  constitute 
a  peculiar  genus. 

ZOOIDS. — In  many  of  the  lower  animals  (such  as  the  Corals,  Medusae, 
&c.)  reproduction  takes  place  in  two  ways,  namely,  by  means  of 
eggs  and  by  a  process  of  budding  with  or  without  separation 
from  the  parent  of  the  product  of  the  latter,  which  is  often 
very  different  from  that  of  the  egg.  The  individuality  of  the 
species  is  represented  by  the  whole  of  the  form  produced  be- 
tween two  sexual  reproductions ;  and  these  forms,  which  are 
apparently  individual  animals,  have  been  called  zooids. 


INDEX. 


AIir.URANT. 


BALANCEMENT. 


A. 

Antarctic  islands,  ancient  flora  of, 

ii.  190. 

ABERRANT  groups,  ii.  227. 
Abyssinia,  plants  of,  ii.  167. 
Acclimatisation,  i.  173. 

Antechinus,  ii.  219. 
Ants  attending  aphides,  i.  323. 
,  slave-making  instinct,  i.  336. 

Adoxa,  i.  270. 

,  neuters,  structure  of,  i.  859. 

Affinities  of  extinct  species,  ii.  106. 

Apes,   not   having   acquired   intel- 

  of  organic  beings,  ii.  225. 
Agassiz,  on  Amblyopsis,  i.  173. 
,  on  groups  of  species  suddenly 

lectual  powers,  i.  282. 
Aphides,  attended  by  ante,  i.  323. 
Aphis,  development  of,  ii.  245. 

appearing,  ii.  88. 

Apteryx,  i.  218. 

,  on  prophetic  forms,  ii.  107. 

Arab  horses,  i.  40. 

,  on  emoryological  succession, 

Aralo-Caspian  Sea,  ii.  121. 

ii.  120. 

Archeopteryx,  ii.  80. 

,  on  the  Glacial  period,  ii.  151. 

Archiac,  M.  de,  on  the  succession  of 

,  on  embryological  characters, 

species,  ii.  103. 

ii.  210. 

Artichoke,  Jerusalem,  i.  176. 

,  on  the  latest  tertiary  forms,  ii. 

Ascension,  plants  of,  ii.  178. 

71. 
.  on  parallelism  of  embryologi- 
cal development  and  geological 

Asclepias,  pollen  of,  i.  236. 
Asparagus,  ii.  143. 
Aspicarpa,  ii.  209. 

succession,  ii.  254. 

Asses,  striped,  i.  198. 

,  Alex.,  on  pedicellarise,  i.  298. 
Algie  of  New  Zealand,  ii.  164. 

,  improved  by  selection,  i.  48. 
Ateuchus,  i.  168. 

Alligators,  males,  fighting,  i.  108. 

Aucapitaine,  on  land-shells,  ii.  187. 

Alternate  generations,  ii.  239. 
Amblyopsis,  blind  fish,  i.  173. 
America,  North,  productions  allied 

Audubon,  on  habits  of  frigate-bird, 
i.  222. 
,  on  variation  in  birds'  nests,  i. 

to  those  of  Europe,  ii.  156. 

324.     ' 

,  ,  boulders  and  glaciers  of, 

,  on  heron  eating  seeds,  ii.  176. 

ii.  159. 

Australia,  animals  of,  i.  140. 

,  South,  no  modern  formations 

,  dogs  of,  i.  328. 

on  west  coast,  ii.  61. 

,  extinct  animals  of,  ii.  121. 

Ammonites,  sudden  extinction  of, 

,  European  plants  in,  ii.  163. 

ii.  99. 

,  glaciers  of,  ii.  159. 

Anagallis,  sterility  of,  ii.  4. 

Azara,  on  flies  destroying  cattle,  i. 

Analogy  of  variations,  i.  197. 

89. 

Ancylus,  ii.  174. 

Azores,  flora  of,  ii.  149. 

Andaman  Islands  inhabited   by  a 

toad,  ii.  182. 

—  > 

Animals,    not    domesticated    from 

being  variable,  i.  19. 
,  domestic,  descended  from  seve- 
ral stocks,  i.  21. 

Babington,  Mr.,  on  British  plants, 
i.  58. 
Baer,  Von,  standard  of  Highness,  i. 

t  ,  acclimatisation  of,  i.  175. 

151. 

of  Australia,  1.  140. 

,  comparison  of  bee  and  fish,  ii. 

with   thicker  fur  in  cold  cli- 

118. 

mates,  i.  166. 

,  embryonic  similarity  of  the 

,  blind,  in  caves,  i.  172. 

Vertebrata,  ii.  241. 

,  extinct,  of  Australia,  ii.  121. 

Baker,  Sir  S.,  on  the  giraffe,  i.  278. 

Anomina,  i.  361. 

Balancement  of  growth,  i.  182. 

323 

324- 


INDEX. 


Baleen,  i.  285. 

Bizcacha,  ii.  133. 

Barberrv,  flowers  of,  i.  121. 
Barrantfe,  M.,  on  Silurian  colonies, 

,  affinities  of,  ii.  227. 
Bladder  for  swimming,  in  fish,  i.  230. 

ii.  90. 

Blindness  of  cave  animals,  i.  170. 

,  on  the  succession  of  species, 

Blyth,  Mr.,  on  distinctness  of  Indian 

ii.  103. 

cattle,  i.  21. 

,  on    parallelism   of  palaeozoic 

,  on  striped  hemionus,  i.  199. 

formations,  ii.  106. 
,  on  affinities  of  ancient  species, 

,  on  crossed  geese,  ii.  10. 
Borrow,  Mr.,  on  the  Spanish  pointer, 

ii.  108. 

i.  40. 

Barriers,  importance  of,  ii.  130. 

Bory  St.  Vincent,  on  Batrachians, 

Bates,  Mr.,  on  mimetic  butterflies, 

ii.  182. 

ii.  222,  223,  224. 

Bosquet,  M.,  on  fossil  Chthamalus, 

Batrachiaus  on  islands,  ii.  182. 

ii.  80. 

Bats,    how    structure    acquired,    i. 

Boulders,  erratic,  on  the  Azores,  ii. 

218. 

149. 

,  distribution  of,  ii.  184. 

Branchiae,!.  231,232. 

Bear,  catching  water-insects,  i.  220. 

of  crustaceans,  i.  238. 

Beauty,  how    acquired,   i.    249;  ii. 

Braun,  Prof.,  on  the  seeds  of  Fuma- 

283.  _ 

riaceae,  i.  271. 

Bee,  sting  of,  i.  255. 

Brent,  Mr.,  on   house-tumblers,  i. 

,  queen,  killing  rivals,  i.  256. 

326. 

,  Australian,  extermination  of, 

Britain,  mammals  of,  ii.  185. 

i.  93. 

Broca,  Prof.,  on  Natural  Selection, 

Bees  fertilising  flowers,  i.  90. 
,  hive,    not   sucking    the    red 

i.  265. 
Bronn,  Prof.,  on  duration  of  specific 

clover,  i.  117. 

forms,  ii.  66. 

,  Ligurian,  i.  117. 
,  hive,  cell-making   instinct,  i. 

,  various  objections  by,  i.  265. 
Brown,  Kobert,  on  classification,  ii. 

342. 

207. 

,  variation  in  habits,  i.  324. 

,  Se"quard,  on  inherited  muti- 

  ,  parasitic,  i.  336. 

lations,  i.  168. 

,  humble,  cells  of,  i.  343. 
Beetles,  wingless,  in  Madeira,  i.  169. 

Busk,  Mr.,  on  the  Polyzoa,  i.  301. 
Butterflies,   mimetic,    ii.    222,    223, 

with  deficient  tarsi,  i.  168. 

224. 

Bentham,  Mr.,  on  British  plants,  i. 

Buzarcingues,  on  sterility  of  varie- 

58. 

ties,  ii.  38. 

,  on  classification,  ii.  211. 

Berkeley,    Mr.,    on    seeds    in    salt 

C. 

water,  ii.  142. 
Bermuda,  birds  of,  ii.  180. 

Cabbage,  varieties  of,  crossed,  i.  122. 
Calceolaria,  ii.  7,  8. 

Birds  acquiring  fear,  i.  325. 

Canary-birds,  sterility  of  hybrids, 

,  beautv  of,  i.  252. 

ii.  9. 

annually  cross  the  Atlantic,  ii. 

Cape  do  Verde  islands,  productions 

150. 

of,  ii.  189. 

,  colour   of,   on    continents,  i. 

,  plants  of,  on  mountains,  ii. 

165. 

162. 

,  footsteps  and  remains  of,  in 
secondary  rocks,  ii.  79. 

Cape  of  Good  Hope,  plants  of,  i. 
158;  ii.  178. 

,  fossil,  in  caves  of  Brazil,  ii. 
121. 

Carpenter,  Dr.,  on  foraminifera,  ii. 
117. 

,    of    Madeira,  Bermuda,   and 

Carthamus,  i.  271. 

Galapagos,  ii.  179,  180. 

Catasetum,  i.  243;  ii.  216. 

,  song  of  males,  i.  109. 

Cats,  with  blue  eyes,  deaf,  i.  13. 

transporting  seeds,  ii.  148. 

,  variation  in  habits  of,  i.  325. 

,  wadern,  ii.  175. 

curling    tail  when  going    to 

,  wingless,  i.  167,  218. 

spring,  i.  254. 

INDEX. 


325 


Cattle  destroying  fir-trees,  i.  88. 
destroyed  by  flies  in  Paraguay, 
i.  89. 

Climbing  plants,  i.  230. 
,  development  of,  i.  305. 
Clover  visited  bv  bees,  i.  117. 

,  breeds  of,  locally  extinct,  i.  134. 

Cobites,  intestine  of,  i.  229. 

,  fertility  of  Indian  and  Euro- 

Cockroach, i.  93. 

pean  breeds,  ii.  10. 

Collections,  palseontologieal,   poor, 

.  Indian,  i.  21  ;  ii.  10. 

ii.  58. 

Cave,  inhabitants  of,  blind,  i.  170. 

Colour,  influenced  by  climate,  i.  165. 

Ceeidomyia,  ii.  239. 

,  in  relation  to  attack  by  flies, 

Celts,   proving   antiquity    of   man, 

i.  248. 

i.  21. 

Columba  livia,  parent  of  domestic 

Centres  of  Creation,  ii.  135. 

pigeons,  i.  26. 

Cephalopoda;,  structures  of  eyes,  i. 

Colymbetes,  ii.  174 

236. 
,  development  of,  ii.  244. 
Cercopithecus,  tail  of,  i.  294. 

Compensation  of  growth,  i.  182. 
Composite,  flowers  and  seeds  of,  i. 
179. 

Ceroxylus  laceratus,  i.  284. 

,  outer  and  inner  florets  of,  i. 

Cervulus,  ii.  9. 

270. 

Cetacea,  teeth  and  hair,  1.  179. 

,  male  flowers  of,  ii.  257. 

,  development   of  the  whale- 

Conclusion, general,  ii.  293. 

bone,  i.  285. 

Conditions,  slight  changes  in,  fa- 

Cetaceans, i.  285. 

vourable  to  fertility,  ii.  27. 

Ceylon,  plants  of,  ii.  164 
Chalk  formation,  ii.  100. 

Convergence  of  genera,  i.  156. 
Coot  i.  222. 

Characters,  divergence  of,  i.  134 

Cope,  Prof.,  on  the  acceleration  or 

,  sexual,  variable,  i.  185,  191. 
,  adaptive  or  analogical,  ii.  218. 

retardation  of  the  period  of  repro- 
duction, i.  232. 

Charlock,  i.  94. 

Coral-islands,  seeds  drifted  to,  ii. 

Checks,  to  increase,  i.  83. 

145. 

,  mutual,  i.  86. 
Chelae  of  Crustaceans,  i.  300. 

reefs,  indicating  movements  of 
earth,  ii.  145. 

Chickens,  instinctive  tameness  of, 

Corn-crake,  i.  223. 

i.  329. 

Correlated    variation    in    domestic 

Chironomus,  its  asexual  reproduc- 

productions, i.  13. 

tion,  ii.  240. 

CoryaiUhes,  i.  241. 

Chthamalina;,  ii.  59. 
Chthamalus,  cretacean  species  of, 

Creation,  single  centres  of,  ii.  135. 
Crinum,  ii.  6. 

ii.  81. 

Croll,  Mr.,  on  subaerial  denudation, 

Circumstances  favourable  to  selec- 

ii. 53,  56. 

tion  of  domestic  products,  i.  46. 

,  on  the  age  of  our  oldest  for- 

  to  natural  selection,  i.  124. 

mations,  ii.  83. 

Cirri  pedes  capable  of  crossing,  i.  124 
,  carapace  aborted,  i.  184". 

,  on   alternate  Glacial  periods 
in  the  North  and  South,  ii.  160. 

,  their  ovitrcrous  frena,  i.  232. 
,  fossil,  ii.  80. 

Crosses,  reciprocal,  ii.  14. 
Crossing  of  domestic  animals,  im- 

  ,  larva;  of,  ii.  243. 
Claparede,  Prof.,  on  the  hair-clasp- 

portance  in  altering  breeds,  i.  23. 
,  advantages  of,  j.  119,  120. 

ers  of  the  Acarido?,  i.  239. 

,  unfavourable   to  selection,  i. 

Clarke,  Kev.  W.  B.,  on  old  glaciers 

125. 

in  Australia,  ii.  159. 

Cniger,  Dr.,  on  Coryanthes,  i.  241. 

Classification,  ii.  202. 

Crustacea  of  New  Zealand,  ii.  164. 

Clift,  Mr.,  on  the  succession  of  types, 

Crustacean,  blind,  i.  171. 

ii.  121. 

air-breathers,  i.  238. 

Climate,  effects  of,  in  checking  in- 

Crustaceans, their  chela;,  i.  300. 

crease  of  beings,  i.  84. 

Cryptocerus,  i.  359. 

,  adaptation  of,  to  organisms,  i. 

Ctcnomys,  blind,  i.  170. 

174 

Cuckoo,  instinct  of,  i.  319,  330. 

326 


CUXXIXGHAM. 


INDEX. 


Cunningham,  Mr.,  on  the  flight  of 
the  logger-headed  duck,  i.  167. 
Currants,  grafts  of,  ii.  19. 
Currents  of  sea,  rate  of,  ii.  144. 

Diversification  of  means  for  same 
general  purpose,  i.  240. 
Division,  physiological,  of  labour, 
i.  139. 

Cuvier,  on  conditions  of  existence, 
i.  320. 

Dog,  resemblance  of  jaw  to  that  of 
the  Thylacinus,  ii.  220. 

Cuvier,  on  fossil  monkeys,  ii.  79. 

Dogs,  hairless,  with  imperfect  teeth, 

,  Fred.,  on  instinct,  i.  320. 

i.  14 

Cvclostoma,  resisting  salt  water,  ii. 

descended  from  several  wild 

'187. 

stocks,  i.  22. 

,  domestic  instincts  6f,  i.  327. 

D. 

,  inherited  civilisation  of.  i.  327. 
,  fertility  of  breeds  together,  ii. 

Dana,  Prof.,  on  blind  cave-animals, 

10. 

i.  172. 

,  of  crosses,  ii.  35. 

,  on  relations  of  crustaceans  of 
Japan,  ii.  158. 

,  proportions  of  body  in  differ- 
ent breeds,  when  young,  ii.  247. 

,  on  crustaceans  of  New  Zea- 
land, ii.  164. 

Domestication,  variation  under,  i.  7. 
Double  flowers,  i.  358. 

Dawson,  Dr.,  on  eozoon,  ii.  85. 

Downing,    Mr.,    on    fruit-trees    in 

De  Candolle,  Aug.  Pyr.,  on  struggle 
for  existence,  i.  77. 

America,  i.  104 
Dragon  flies,  intestines  of,  i.  229. 

,  on  nrnbelliferee,  i.  181. 

Drift-timber,  ii.  145. 

,  on  general  affinities,  ii.  228. 

Driver-ant,  i.  361. 

,  Alph.,  on  the  variability  of 
oaks,  i.  62. 

Drones  killed  by  other  bees,  i.  256. 
Duck,  domestic,  wings  of,  reduced, 

,  on   low  plants,   widely  dis- 

i. 12. 

persed,  ii.  196. 

,  beak  of,  i.  285. 

,  on  widely-ranging  plants  be- 
ing variable,  i.  67. 

,  logger-headed,  i.  218. 
Duckweed,  ii.  173. 

,  on  naturalisation,  i.  139. 

Dugong,  affinities  of,  ii.  206. 

,  on  winged  seeds,  i.  181. 

Dung-beetles  with  deficient  tarsi,  L 

,  on  Alpine  species  suddenly 
becoming  rare,  i.  210. 

168. 
Dytiscus,  ii.  174 

,  on  distribution  of  plants  with 

large  seeds,  ii.  145. 

,  on  vegetation  of  Australia,  ii. 

167. 

Earl,  Mr.  W.,  on  the  Malay  Archi- 

  ,  on  fresh-  water  plants,  ii.  174 

pelago,  ii.  185. 

,  on  insular  plants,  ii.  178. 
Degradation  of  rocks,  ii.  52. 

Ears,  drooping,  in    domestic   ani- 
mals, i.  13. 

Denudation,  rate  of,  ii.  54 

,  rudimentary,  ii.  261. 

of  oldest  rocks,  ii.  85. 

Earth,  seeds  in  roots  of  trees,  ii. 

of  granitic  areas,  ii.  64. 

145. 

Development  of  ancient  forms,  ii. 

charged  with  seeds,  ii.  148. 

116. 
Devonian  svstem,  ii.  113. 

Echinodermata,  their  pedicel  ariae, 
i.  297. 

Dianthus,  fertility  of  crosses,  ii.  13. 

Eciton,  i.  359. 

Dimorphism  in  plants,  i.  55;  ii.  29. 
Dirt  on  feet  of  birds,  ii.  148. 

Economy  of  organisation,  i.  182. 
Edentata,  teeth  and  hair,  i.  179. 

Dispersal,  means  of,  ii.  140. 

,  fossil  species  of,  ii.  288. 

during  Glacial  period,  ii.  151. 
Distribution,  geographical,  ii.  129. 

Edwards,  Milne,  on   physiological 
division  of  labour,  i.  139. 

•  ,  means  of,  ii.  140. 
Disuse,  effect  of,  under  nature,  i. 

,  on  gradations  of  structure,  i. 
244. 

167. 
Divergence  of  character,  L  134 

,  on  embryological  characters, 
ii.  210. 

INDEX.  FRIGATE-BIRD. 


327 


Eggs,  young  birds  escaping  from,  i. 

Fishes,  of  southern  hemisphere,  ii. 

106. 

164. 

Egypt,  productions  of,  not  modified, 
i.  263. 

Flat-fish,  their  structure,  i.  290. 
Flight,  powers  of,  how  acquired,  i. 

Electric  organs,  i.  234. 
Elephant,  rate  of  increase,  i.  80. 
,  of  Glacial  period,  i.  176. 

Flint-tools,    proving    antiquity    of 
man,  i.  21. 

Embryology,  ii.  239;> 

Flower,  Prof.,  on  the  Larynx,  i.  297. 

Eozoon  Canadense,  ii.  84. 

,  on  Halitherium,  ii.  108. 

Epilepsy  inherited,  i.  167. 

,  on  the  resemblance  between 

Existence,  struggle  for,  i.  75. 
,  condition  of,  i.  261. 

the  jaws  of  the  dog  and  Thyla- 
cinus,  ii.  220. 

Extinction,  as  bearing  on  natural 
selection,  i.  150. 

,  on  the  homology  of  the  feet  of 
certain  marsupials,  ii.  232. 

of  domestic  varieties,  L  145. 

Flowers,  structure  of,  in  relation  to 

,  ii.  94. 

crossing,  i.  114. 

Eye,  structure  of,  i.  225. 
—  *  —  ,  correction  for  aberration,  i.  255. 

,  of  composite  and    umbelli- 
iferffi,  i.  179,  270. 

Eyes,  reduction  in  moles,  i.  170. 

,  beauty  of,  i.  252. 

,  double,  i.  358. 

F. 

Flysch  formation,  destitute  of  or- 

ganic remains,  ii.  59. 

Fabrc,  M.,  on  hymenoptera  fight- 

Forbes, Mr.  D.,  on  glacial  action  in 

ing,  i.  108.  , 

the  Andes,  ii.  160. 

,  on  parasitic  sphex,  i.  336. 
,  on  Sitaris,  ii.  252. 

,  E.,  on  colours  of  shells,  i.  165. 
,  on  abrupt  range  of  shells  in 

Falconer,  Dr.,  on  naturalisation  of 

depth,  i.  210. 

plants  in  India,  i.  80. 
,  on  elephants  and  mastodons, 

,  on  poorness  of  palueontological 
collections,  ii.  58. 

ii.  113. 

,  on  continuous  succession  of 

and  Cautley,  on  mammals  of 

genera,  ii.  93. 

sub-Himalayan  beds,  ii.  122. 

,  on  continental  extensions,  ii. 

Falkland  Islands,  wolf  of,  ii.  183. 
Faults,  ii.  54. 

140.  141. 
,  on  distribution  during  Glacial 

Faunas,  marine,  ii.  131. 

period,  ii.  152. 

Fear,  instinctive,  in  birds,  i.  329. 

,  on  parallelism  in  time  and 

Feet  of  birds,  young  molluscs  ad- 
hering to,  ii.  174. 

space,  ii.  200. 
Forests,  changes  in,  in  America,  i. 

Fertilisation  variously    effected,  i. 

91. 

241,  252. 

Formation,  Devonian,  ii.  113. 

Fertility  of  hybrids,  ii.  6. 
—  '  —  ,  from  slight  changes  in  condi- 

  ,  Cambrian,  ii.  84. 
Formations,  thickness  of,  in  Britain, 

tions,  ii  28. 

ii.  55. 

of  crossed  varieties,  ii.  34. 
Fir-trees  destroyed  by  cattle,  i.  88. 
,  pollen  of,  i.  257. 

,  intermittent,  ii.  69. 
Formica,  rufescens,  i.  336. 
,  Bangui  nea,  i.  338. 

Fish,  flying,  i.  218. 

,  flava.  neuter  of,  i.  360. 

,  te'leostean,  sudden  appearance 

Forms,  lowly  organised,  long  en- 

of, ii.  81. 

during,  i.  154. 

,  eating  seeds,  ii.  14fi,  175. 
,   fresh-water,  distribution    of, 

Frena,  ovigerous,  of  cirripedes,  i. 
232. 

ii.  17'2. 

Fresh-water  productions,  dispersal 

Fishes,   ganoid,   now    confined    to 

of,  ii.  171. 

fresh  water,  i.  130. 

Fries,  on  species  in  large  genera 

•  ,  electric  organs  of,  i.  234. 

being  closely  allied  to  other  spe- 

  ,  ganoid,  living  in  fresh  water, 

cies,  i.  71. 

ii.  99. 

Frigate-bird,  i.  222. 

IXDEX. 


HABIT. 


Frogs  on  islands,  ii.  182. 

Glacial  period,  affecting  the  North 

Fruit-trees,    gradual    improvement 
of,  i.  42. 

and  South,  ii.  158. 
Glands,  mammary,  i.  295. 

in  United  States,  i.  104. 

Gmelin,  on  distribution,  ii.  151. 

,  varieties  of,  acclimatised  in 

Godwin-  Austen,  Mr.,  on  the  Malay 

United  States,  i.  176. 

Archipelago,  ii.  74. 

Fuci,  crossed,  ii.  15,  23. 
Fur,  thicker  in  cold  climates,  i.  166. 

Goethe,  on  compensation  of  growth, 
i.  182. 

Furze,  ii.  241. 

Gomphia,  i.  272. 

Gooseberry,  grafts  of,  ii.  19. 

G. 

Gould,  Dr.  Aug.  A.,  on  land-shells, 

ii.  186. 

Galapagos    Archipelago,   birds    of, 
ii.  179. 

,  Mr.,  on  colours  of  birds,  i.  165. 
,  on  instincts  of  cuckoo,  i.  333. 

,  productions  of,  ii.  188,  190. 
Galaxias,  its  wide  range,  ii.  172. 
Galeopithecus,  i.  217. 
Game,  increase  of,  checked  by  ver- 
min, i.  86. 

,  on  distribution  of  genera  of 
birds,  ii.  195. 
Gourds,  crossed,  ii.  38. 
Graba,  on  the  Uria  lacrymas,  i.  113. 
Grafting,  capacity  of,  ii.  18,  19,  20. 

Gartner,  on  sterility  of  hybrids,  ii. 
3,  4,  11. 

Granite,  areas  of  denuded,  ii.  64. 
Grasses,  varieties  of,  i.  137. 

,  on  reciprocal  crosses,  ii.  15. 
,  on  crossed  maize  and  verbas- 

Gray,  Dr.  Asa,  on  the  variability  of 
oaks,  i.  62. 

cum,  ii.  37. 

,  on  man  not  causing  variabil- 

,  on  comparison  of  hybrids  and 
mongrels,  ii.  40,  41,  42. 
Gaudry,  Prof.,  on  intermediate  ge- 

itv, i.  98. 
-,  on  sexes  of  the  holly,  i.  116. 
,  on  trees  of  the  United  States, 

nera  of  fossil  mammals  in  Attica, 

i.  123. 

ii.  107. 

,  on  naturalised  plants  in  the 

Geese,  fertility  when  crossed,  ii.  9, 

United  States,  i.  139. 

10. 

,  on  aestivation,  i.  272. 

,  upland,  i.  222. 

,  on  Alpine  plants,  ii.  151. 

Geikie,  Mr.,  on  subaerial  denuda- 

  ,  on  rarity  of  intermediate  va- 

tion, ii.  53. 

rieties,  i.  212. 

Genealogy,  important  in  classifica- 

  ,  Dr.  J.  E.,  on  striped  mule,  i. 

tion,  ii.  212. 

199. 

Generations,  alternate,  ii.  239. 

Grebe,  i.  221. 

Geoffroy    St.  Hilaire,  on  balance- 

Grimm,  on  asexual  reproduction,  ii. 

merit,  i.  182. 

240. 

,  on  homologous  organs,  ii.  233. 
,  Isidore,  on  variability  of  re- 
peated parts,  i.  184 
,  or  correlation,  in  monstrosi- 
ties, i.  13. 

Groups,  aberrant,  ii.  227. 
Grouse,  colours  of,  i.  104. 
,  red,  a  doubtful  species,  i.  59. 
Growth,  compensation  of,  i.  182. 
Giinther,  Dr.,  on  flat-fish,  i.  292. 

,  on  correlation,  i.  179. 
,  on  variable  parts  being  often 

,  on  prehensile  tails,  i.  295. 
,  on  the  fishes  of  Panama,  ii. 

monstrous,  i.  190. 

131. 

Geographical  distribution,  ii.  129. 

,  on  the  range  of  fresh-water 

Geography,  ancient,  ii.  303. 
Geology,  future  progress  of,  ii.  302. 
,  imperfection  of  the  record,  ii. 

fishes,  ii.  172. 
,  on  the  limbs  of  Lepidosiren, 
ii.  258. 

303. 

II. 

Gervais,  Prof.,  on  Typotherium,  ii. 
108. 

Haast,  Dr.,  on  glaciers  of  New  Zea- 

Giraffe, tail  of,  i.  245. 

land,  ii.  159. 

.  structure  of,  i.  276. 

Habit,  efl'ect  of,  under  domestica- 

Glacial period,  ii.  151. 

tion,  i.  12. 

INDEX. 


329 


Habit,  effect  of,  under  nature,  i.  168. 

,  diversified,  of  same  species, 

i.  219. 

Hiickel,  Prof.,  on  classification  and 
the  lines  of  descent,  ii.  231. 

Hair  and  teeth,  correlated,  i.  179. 

Halitherium,  ii.  108. 

Harcourt,  Mr.  E.  V.,  on  the  birds  of 
Madeira,  ii.  180. 

Ilartung,  M.,  on  boulders  in  the 
Azores,  ii.  149. 

Hazel-nuts,  ii.  143. 

Hearne,  on  habits  of  bears,  i.  220. 

Heath,  changes  in  vegetation,  i. 
87. 

Hector,  Dr.,  on  glaciers  of  New  Zea- 
land, ii.  159. 

Heer,  Oswald,  on  ancient  cultivated 
plants,  i.  20. 

-,  on  plants  of  Madeira,  i.  130. 

Helianthemum,  i.  272, 

Helix  pomatia,  ii.  187. 

,  resisting  .salt  water,  ii.  187. 

Helmholtz,  M.,  on  the  imperfection 
of  the  human  eye,  i.  255. 

Helosciadium,  ii.  143. 

Hemionus,  striped,  i.  202. 

Hensen,  Dr.,  on  the  eyes  of  Cepha- 
lopoda, i.  237. 

Herbert,  W.,  on  struggle  for  exist- 
ence, i.  77. 

,  on  sterility  of  hybrids,  ii.  6. 

Hermaphrodites  cross'iug,  i.  119. 

Heron  eating  seed,  ii.  176. 

Heron,  Sir  K.,  on  peacocks,  i.  109. 

Heusinger,  on  white  animals  poi- 
soned by  certain  plants,  i.  13. 

Hewitt,  ftlr.,  on  sterility  of  first 
crosses,  ii.  23. 

Hildebrand,  Prof.,  on  the  self-ste- 
rility of  Corydalis,  ii.  7. 

Hilgendorf,  on  intermediate  varie- 
ties, ii.  66. 

Himalaya,  glaciers  of,  ii.  159, 

,  plants  of,  ii.  Ifi2. 

Hippeastrum,  ii.  7. 

Hippocampus,  i.  295. 

Hofmeister,  Prof.,  on  the  move- 
ments of  plants,  i.  308. 

Holly-trees,  sexes  of,  i.  115. 

Hooker,  Dr.,  on  trees  of  New  Zea- 
land, i.  123. 

,  on  acclimatisation  of  Hima- 
layan trees,  i.  174. 

",  on  flowers  of  urnbelliferse,  i. 

180. 

,  on  the  position  of  ovules,  i.  268. 

47 


Hooker,  Dr..  on  glaciers  of  Himala- 
ya, ii.  159. 

,  on  algse  of  New  Zealand,  ii. 

164. 

,  on  vegetation  at  the  base  of 

the  Himalaya,  ii.  164. 

,  on  plants  of  Tierra  del  Fuego, 

ii.lGl. 

,  on  Australian  plants,  ii.  163, 

190. 

,  on  relations  of  flora  of  Amer- 
ica, ii.  167. 

,  on  flora  of  the  Antarctic  lands, 

ii.  169,189. 

,  on  the  plants  of  the  Gala- 
pagos, ii.  181, 188. 

,  on  glaciers  of  the  Lebanon, 

ii.  159. 

,  on  man  not  causing  variabil- 
ity, i.  97. 

,  on  plants  of  mountains  of 

Fernando  Po,  ii.  162. 

Hooks  on  palms,  i.  247. 

on  seeds,  on  islands,  ii.  181. 

Hopkins,  Mr.,  on  denudation,  ii.  63. 

Hornbill,  remarkable  instinct  of,  i. 
364. 

Horns,  rudimentary,  ii.  261. 

Horse,  fossil,  in  La  Plata,  ii.  96. 

,  proportions  of,  when  young, 

ii.  247. 

Horses  destroyed  by  flies  in  Para- 
guay, i.  89. 

.  striped,  i.  199. 

Horticulturists,  selection  applied  by, 
i.  37. 

Huber,  on  cells  of  bees,  i.  349. 

' ,  P.,  on  reason  blended  with 

instinct,  i.  320. 

,  on  habitual  nature  of  instincts, 

i.  320. 

-™ — ,  on  slave-making  ante,  i.  336. 

-. ,  on  Melipona  domestica,  i.  343. 

Hudson,  Mr.,  on  the  Ground- Wood- 
pecker of  La  Plata,  i.  221. 

— — ,  on  the  Molothrus,  i.  334. 

Humble-bees,  cells  of,  i.  343. 

Hunter,  J.,  on  secondary  sexual 
characters,  i.  185. 

Hutton,  Captain,  on  crossed  geese, 
ii.  10. 

Huxley,  Prof.,  on  structure  of  her- 
maphrodites, i.  124. 

,  on  the  affinities  of  the  Sirenia, 

ii.  108. 

,  on  forms  connecting  birds  and 

reptiles,  ii.  108. 


330 


INDEX.         LOBELIA   FULGEXS.' 


Huxley,  Prof.,  on  homologous  or- 

Kidney-bean, acclimatisation  of,  i. 

gans,  ii.  233. 
,  on  the  development  of  aphis, 
ii.  245. 

177. 
Kidneys  of  birds,  i.  178. 
Kirby,  on  tarsi  deficient  in  beetles, 

Hybrids  and  mongrels  compared,  ii. 
39. 

i.  163. 
Knight,  Andrew,  on  cause  of  varia- 

Hybridism, ii.  1. 

tion,  i.  8. 

Hydra,  structure  of,  i.  229. 
Hvmenoptera,  fighting,  i.  108. 
Hvmenopterous  msect,diviug,  i.  222. 
Hyoseris,  i.  271. 

Kolreuter,  on  Intercrossing,  i.  119. 
,  on  the  barberrv,  i.  121. 
,  on  sterility  of  "hybrids,  ii.  3,  4. 
,  on  reciprocal  crosses,  ii.  15. 
,  on  crossed  varieties  of  nico- 

_ 

tiana,  ii.  38. 

,  on  crossing  male  and  herma- 

Ibla, i.  183. 

phrodite  flowers,  ii.  256. 

Icebergs  transporting  seeds,  ii.  148. 

Increase,  rate  of,  i.  79. 

L. 

Individuals,  numbers  favourable  to 

selection,  i.  124. 
,  many,  whether  simultaneously 

Lamarck,  on  adaptive  characters,  ii. 
218. 

created,  ii.  139. 

Lancelot,  i.  154 

Inheritance,  laws  of,  i.  15. 

,  eyes  of,  i.  227. 

,  at  corresponding  ages,  L  15, 

Landois,  on  the  development  of  the 

105. 

wings  of  insects,  i.  231. 

Insects,  colour  of,  fitted  for  their 

Land-shells,  distribution  of,  ii.  186. 

stations,  i.  103. 

,  of   Madeira,    naturalised,    ii. 

,  sea-side,  colours  of,  i.  165. 

193. 

,  blind,  in  caves,  i.  171. 

,  resisting  salt  water,  ii.  1  87. 

,  luminous,  i.  236. 
,  their  resemblance  to  certain 

Languages,  classification  of,  ii.  214. 
Lankester.  Mr.  E.  Kay,  on  Longe- 

objects, i.  283. 

vity,  i.  263. 

,  neuter,  i.  359. 

,*on  homologies,  ii.  237. 

Instinct,  i.  319. 
,  not  varying   simultaneously 

Lapse,  great,  of  time,  ii.  51. 
Larvae,  ii.  241,  242,  243. 

with  structure,  i.  357. 

Laurel,  nectar  secreted  by  the  leaves, 

Instincts,  domestic,  i.  325. 

i.  114. 

Intercrossing,  advantages  of,  i.  149, 

Laurentian  formation,  ii.  84. 

ii.  27. 

Laws  of  variation,  i.  164. 

Islands,  oceanic,  ii.  177. 

Leech,  varieties  of,  i.  93. 

Isolation  favourable  to  selection,  i. 

Leguminosse,    nectar    secreted    by 

127. 

glands,  i.  114. 

J. 

Leibnitz1  attack  on  Newton,  ii.  294. 

Lepidosiren,  i.  130  ;  ii.  109. 

Japan,  productions  of,  ii.  158. 

,  limbs  in  a  nascent  condition, 

Java,  plants  of,  ii.  162. 

ii.  258. 

Jones,  Mr.  J.  M.,  on  the  birds  of 

Lewes,  Mr.  G.  II.,  on  species  not 

Bermuda,  ii.  180. 
Jourdain,  M.,  on  the  eye-spots  of 
star-fishes,  i.  225. 
Jukes.  Prof.,  on  subaerial  denuda- 

having changed  in  Egypt,  i.  263. 
,  on  the  Salamandra  atra,  ii.  256. 
,  on  many  forms  of  life  having 
been  at  first  evolved,  ii.  300. 

tion,  ii.  53. 

Life,  strutrjrle  for,  i.  77. 

Jussieu,  on  classification,  ii.  209. 
K. 

Lingula.  Silurian,  ii.  83. 
Linmeus,  aphorism  of,  ii.  205. 
Lion,  mane  of,  i.  109. 

,  vouns  of,  striped,  ii.  241. 

Kentucky,  caves  of,  i.  172. 
Kerguelcn-land,  flora  of,  ii.  169,  189. 

Lobefia  fulgens,  i.  90,  121. 
,  sterility  of  crosses,  ii.  7. 

LOCKWOOD. 


INDEX. 


331 


Lockwood,  Mr.,  on  the  ova  of  the 

Hippocampus,  i.  295. 

. 

Locusts  transporting  seeds,  ii.  147. 
Logan,  Sir  W.,  oil  Laurentian  for- 

Mncleay,  on  analogical  characters, 
ii.  218. 

mution,  ii.  84. 

Macrauchenia,  ii.  107. 

Lowe,  Kev.  K.  T.,  on  locusts  visiting 
Madeira,  ii.  147. 

M'l  )<>nnell,  Dr.,  on  electric  organs, 

i.  •_':;•». 

Lowness  of  structure  connected  with 

Madeira,  plants  of.  i.  130. 

variability,  i.  1S4. 
,  related  to  wide  distribution,  ii. 

,  beetles  of,  wingless,  i.  169. 
,  fossil  land-shells  of,  ii.  121. 

19H. 

,  birds  of,  ii.  180. 

Lubbock,  Sir  J.,  on  the  nerves  of 

Magpie  tame  in  Norway,  i.  325. 

coccus,  i.  54. 
,  on  secondary  sexual  charac- 

Males lighting,  i.  108. 
Maize,  crossed,  ii.  37. 

ters,  i.  193. 
,  on  a  diving  hymenopterous 

Malay  Archipelago  compared  with 
Europe,  ii.  74. 

insect,  i.  222. 

,  mammals  of,  ii.  185. 

,  on  affinities,  ii.  73. 

Malm,  on  flat-fish,  i.  291. 

,  on  metamorphoses,  ii.  239,  242. 
Lucas,  Dr.  P.,  on  inheritance,  i.  14. 

Malpighiaceee,  small  imperfect  flow- 
ers of,  i.  269. 

,  on  resemblance  of  child  to 

,  ii.  209. 

parent,  ii.  43. 
Lund  and   Clausen,  on    fossils  of 

Mammae,  their  development,  i.  295. 
,  rudimentary,  ii.  255. 

Brazil,  ii.  121. 

Mammals,  fossil,  in  secondary  for- 

Lyell, Sir  C.,  on  the  struggle  for 

mation,  ii.  79. 

existence,  i.  77. 

,  insular,  ii.  188. 

,  on  modern    changes  of  the 

Man,  origin  of,  ii.  304. 

earth,  i.  118. 

Manatee,  rudimentary  nails  of,  ii. 

,  on  terrestrial  animals  not  hav- 

260. 

ing  been  developed  on  islands,  i. 

Marsupials  of  Australia,  i.  140. 

281. 

,  structure  of  their  feet,  ii.  232. 

,  on  a  carboniferous  land-shell. 

,  fossil  species  of,  ii.  121. 

ii.  59. 

Martens,  M.,  experiment  on  seeds, 

,  on  strata  beneath  Silurian  sys- 

ii. 144. 

tem,  ii.  84. 

Martin,  Mr.  W.  C.,  on  striped  mules, 

,  on  the  imperfection  of  the  geo- 

i. 201. 

logical  record,  ii.  88. 

Masters,  Dr.,  on  Saponaria,  i.  272. 

,  on  the  appearance  of  species, 

Matteucci,  on  the  electric  organs  of 

ii.  88. 
,  on  Barrande's  colonies,  ii.  90. 

rays,  i.  234. 
Matthiola,  reciprocal  crosses  of,  ii. 

,    on    tertiary    formations    of 

15. 

Europe  and   North  America,  ii. 

Maurandia,  i.  307. 

101. 
,  on  parallelism  of  tertiary  for- 

Means of  dispersal,  ii.  140. 
Melipona  domestica,  i.  343. 

mations,  ii.  106. 

Merrcll,    Dr.,    on    the    American 

,  on  transport  of  seeds  by  ice- 

cuckoo, i.  330. 

bergs,  ii.  148. 
,  on  great  alterations  of  climate, 
ii.  170. 

Metamorphism  of  oldest  rocks,  ii.  85. 
Mice  destroying  bees,  i.  90. 
,  acclimatisation  of,  i.  175. 

,  on  the  distribution  of  fresh- 

  ,  tails  of,  i.  294. 

water  shells,  ii.  174. 

Miller,  Prof.,  on  the  cells  of  bees,  i. 

,  on  land-shells  of  Madeira,  ii. 

344,  350. 

193. 

Mirabilm,  crosses  of,  ii.  15. 

Lyell  and  Dawson,  on  fossilized  trees 

Missel-thrush,  i.  93. 

'in  Nova  Scotia,  ii.  7<». 
Lvthrum    salicaria,  trimorphic,  ii. 

Mistletoe,  complex  relations  of.  i.  3. 
Mivart,  Mr.,  on  the  relation  ol  hair 

32. 

and  teeth,  i.  179. 

332 


INDEX. 


Mivart,  Mr.,  on  the  eyes  of.cephalo- 

Murray,  Mr.    A.,  on  cave-insects, 

pods,  i.  237. 

i.  173. 

.various  objections  to  Natural 

Mustela  vision,  i.  216. 

Selection,  i.  275. 

Myanthus,  ii.  216. 

,  on  abrupt  modifications,  i.  313. 
,   on    the    resemblance  of   the 

Myrmecocystus,  i.  359. 
Myrmica,  eyes  of,  i.  361. 

mouse  and  antechinus,  ii.  218. 

Mocking-thrush  of  the  Galapagos, 

N. 

ii.  193. 
Modification  of  species  not  abrupt, 

Nageli,  on  morphological  characters, 

ii.  298. 

i.  266. 

Moles,  blind,  i.  170. 
Molothrus,  habits  of,  i.  334. 

Nails,  rudimentary,  ii.  260. 
Nathusius,  Von,  on  pigs,  i.  249. 

Mongrels,  fertility  and  sterility  of, 

Natural  history,  future  progress  of, 

ii.  34. 

ii.  301. 

and  hybrids  compared,  ii.  39. 
Monkeys,  fossil,  ii.  79. 

selection,  i.  97. 
system,  ii.  201. 

Monachanthus,  ii.  216. 

Naturalisation    of    forms    distinct 

Mons,  Van,  on  the  origin  of  fruit- 
trees,  i.  33. 

from  the  indigenous  species,  i.  138. 
Naturalisation  in  New  Zealand,  i. 

Monstrosities,  i.  51. 

255. 

Moquin-Tandon,  on  sea-side  plants, 

Naudin,  on  analogous  variations  in 

i.  166. 

gourds,  i.  195. 

Morphology,  ii.  231. 

,  on  hybrid  gourds,  ii.  38. 

Morren,  on  the  leaves  of  Oxalis,  i. 

,  on  reversion,  ii.  4i. 

308. 
Moths,  hybrid,  ii.  9. 

Nautilus,  Silurian,  ii.  83. 
Nectar  of  plants,  i.  114. 

Mozart,  musical  powers  of,  i.  321. 
Mud,  seeds  in,  ii.  175. 

Nectaries,  how  formed,  i.  114. 
Nelumbium  luteum,  ii.  176. 

Mules,  striped,  i.  201. 

Nests,  variations  in,  i.  324,  355,  364. 

Muller,  Adolf,  on  the  instincts  of  the 

Neuter  insects,  i.  359,  360. 

cuckoo,  i.  331. 

Newman,  Col.,  on  humble-bees,  i.  90. 

Muller,  Dr.  Ferdinand,  on  Alpine 

New  Zealand,  productions  of,  not 

Australian  plants,  ii.  163. 
Muller,  Fritz,  on  dimorphic  crusta- 
ceans, i.  55,  362. 

perfect,  i.  255. 
,  naturalised  products  of,  ii.  119. 
,  fossil  birds  of,  ii.  121. 

,  on  the  lancelet,  i.  154. 

,  glaciers  of,  ii.  159. 

,  on  air-breathing  crustaceans, 

,  crustaceans  of,  ii.  164. 

i.  238. 

,  algae  of,  ii.  1(54. 

,  on  climbing  plants,  i.  307. 
,  on  the  self-sterility  of  orchids, 

,  number  of  plants  of,  ii.  178. 
,  flora  of,  ii.  189. 

ii.  7. 

Newton,  Sir  I.,  attacked  for  irre- 

,  on  embryology  in  relation  to 

ligion,  ii.  294. 

classification,  ii.  210. 

,  Prof.,  on  earth  attached  to  a 

,  on  the  metamorphoses  of  crus- 
taceans, ii.  245,  253. 

partridge's  foot,  ii.  148. 
Nicotiana,  crossed  varieties  of,  ii.  39. 

,  on  terrestrial  and  fresh-water 

,  certain  species  very  sterile,  ii. 

organisms    not    undergoing    any 
metamorphosis,  ii.  250. 
Multiplication  of  species  not  indefi  - 

14. 
Nitsche,  Dr.,  on  the  Polyzoa,  i.  301. 
Noble,  Mr.,  on  fertility  of  Rhodo- 

nite, i.  157. 

dendron,  ii.  8. 

Murchison,  Sir  R.,  on  the  forma- 
tions of  Russia,  ii.  60. 

Nodules,  phosphatic,  in  azoic  rocks, 
ii.  84. 

,  on  azoic  formations,  ii.  84. 

,  on  extinction,  ii.  94. 

. 

Murio,  Dr.,  on  the  modification  of 
the  skull  in  old  age,  i.  233. 

Oaks,  variability  of,  i.  62. 
Onites,  appelles,  i.  108. 

INDEX. 


PLANTS. 


333 


Ouonis,  small  imperfect  flowers  of, 

Palm  with  hooks,  i.  247. 

i.  209. 

Papaper  bructc-atum,  i.  -J72. 

Orohids,  fertilisation  of,  i.  241. 

Paraguay,  cattle  destroyed  by  flies, 

,    the    development    of    their 

i.  89. 

flowers,  i.  303. 

Parasites,  i.  334. 

,  forms  of,  ii.  216. 

Partridge,  with   ball  of  earth  at- 

Orchis, pollen  of,  i.  236. 

tached  to  foot,  ii.  148. 

Organisation,  tendency  to  ad  vance, 

Parts  greatly  developed,  variable, 

i.  151. 

L  185. 

Organs  of  extreme  perfection,  i.  223. 
,  electric,  of  tislies,  i.  234. 

Parus  major,  L  220. 
Passiflora,  ii.  7. 

of  little  importance,  i.  245. 

Peaches  in  United  States,  i.  104. 

,  homologous,  ii.  233. 

Pear,  grafts  of,  ii.  18. 

,  rudiments  of,  and  nascent,  ii. 

Pedicellaria,  i.  298. 

255. 
<  )rnithorhynchus,  i.  130;  ii.  208. 

Pelagornium,  flowers  of,  L  180. 
,  sterility  of,  ii.  7. 

,  mamma  of,  i.  296. 

Pelvis  of  women,  i.  178. 

Ostrich  not  capable  of  flight,  i.  281. 
,  habit  of  laying  eggs  together, 
i.  335. 

Peloria,  i.  180. 
Period,  glacial,  ii.  151. 
Petrels,  habits  of,  i.  221. 

,  American,  two  species  of,  ii. 

Phasianus,  fertility  of  hybrids,  ii.  9. 

132. 

Pheasant,  young,  wild,  i.  329. 

Otter,  habits  of,  how  acquired,  i. 

Pictet,  Prof.,  on  groups  of  species 

216. 
Ouzel,  water,  i.  222. 

suddenly  appearing,  ii.  77. 
,  on  rate  ot'orgauic  change,  ii.  90. 

Owen,  Prof.,  on  birds  not  flying,  L 

,  on  continuous  succe.ssion  of 

167. 

genera,  ii.  93. 

,    on    vegetative    repetition,  i. 

,  on  change  in  latest  tertiary 

184. 

forms,  ii.  71. 

,  on    variability  of  unusually 

,  on  close  alliance  of  fossils  in 

developed  parts,  i.  185. 
,  on  the  eyes  of  fishes,  i.  227. 

consecutive  formations,  ii.  114. 
,  on  early  transitional  links,  ii. 

,  on  the  swim-bladder  of  fishes, 

78. 

i.  231. 

Pierce,  Mr.,  on  varieties  of  wolves, 

,  on  fossil  horse  of  La  Plata,  ii. 

i.  111. 

96. 
,  on  generalized  form,  ii.  107. 

Pigeons  with  feathered  feet  and  skin 
between  toes,  i.  14. 

,  on  relation  of  ruminanta  and 

,  breeds  described,  and  origin 

pachyderms,  ii.  107. 
,  on  fossil  birds  of  New  Zea- 

of, i.  23. 
,  breeds  of,  how  produced,  i.  44, 

land,  ii.  121. 

47. 

,  on  succession  of  types,  ii.  121. 
,  on  affinities  of  the  dugong,  ii. 
206. 
,  on  homologous  organs,  ii.  233. 

,  tumbler,  not  being  able  to  get 
out  of  egg,  i.  106. 
,  reverting  to  blue  colour,  i.  197. 
,  instinct  of  tumbling,  i.  327. 

,  on  the  metamorphosis  of  ce- 

,  voung  of,  ii.  248. 

phalopods,  ii.  244. 

Pigs,  'black,  not  affected   by    the 

paint-root,  i.  13. 

P. 

,  modified  by  want  of  exercise, 

i.  24ft. 

Pacific  Ocean,  faunas  of,  ii.  131. 

Pistil,  rudimentary,  ii.  256. 

Pacini,  on  electric  organs,  i.  235. 
Paley,  on  no  organ  formed  to  give 

Plants,  poisonous,  not  affecting  cer- 
tain coloured  animals,  i.  13. 

pain,  i.  254. 

,  selection,  applied  to,  i.  41. 

Pallas,  on  the  fertility  of  the  domes- 
ticated descendants  of  wild  stocks, 

,  gradual  improvement  of,  i.  42. 
,  not  improved    in    barbarous 

ii.10. 

countries,  i.  43. 

334 


INDEX. 


SALT   WATER. 


Plants,  dimorphic,  i.  55  ;  ii.  29. 

Ramond,  on  plants  of  Pyrenees,  ii. 

,  destroyed  by  insects,  i.  83. 

153. 

,   in  midst  of  range,  have  to 

Ramsav,  Prof.,  on  subaerial  denu- 

struggle  with  other  plants,  i.  95. 

datio'n,  ii.  53. 

,  nectar  of,  i.  114. 

,  on  thickness  of  the  British 

,  fleshy,  on  sea-shores,  i.  166. 

formations,  ii.  55,  56. 

,  climbing,  i.  230,  305. 

,  on  faults,  ii.  55. 

,  fresh-water,  distribution  of,  ii. 

Ramsay,  Mr.,  on  instincts  of  cuckoo, 

174. 

i.  333. 

,  low  in  scale,   widely   distri- 

Ratio of  increase,  i.  79. 

buted,  ii.  196. 
Pleuronectidffi,    their   structure,    i. 

Rats  supplanting  each  other,  i.  93. 
,  acclimatisation  of,  i.  175. 

290. 

,  blind,  in  cave,  i.  171. 

Plumage,  laws  of  change  in  sexes 

Rattle-snake,  i.  254. 

of  birds,  i.  109. 
Plums  in  the  United  States,  L  104. 
Pointer  dog,  origin  of,  i.  40. 
,  habits  of,  i.  327. 

Reason  and  instinct,  5.  319. 
Recapitulation,  general,  ii.  267. 
Reciprocity  of  crosses,  ii.  14. 
Record,  geological,  imperfect,  ii.  48. 

Poison  not  affecting  certain  coloured 

Rengger,  on  flies  destroying  cattle, 

animals,  i.  13. 

i.  89. 

,  similar  effect  of,  on  animals 

Reproduction,  rate  of,  i.  79. 

and  plants,  ii.  299. 

Resemblance,  protective,  of  insects, 

Pollen  of  fir-trees,  i.  257. 

i.  283. 

transported  by  various  means, 

to  parents  in  mongrels    and 

i.  241,  252. 

hybrids,  ii.  41. 

Pollinia,  their  development,  i.  304. 

Reversion,    law  of   inheritance,    i. 

Polyzoa,  their  avicularia,  i.  301. 

16. 

Poole,  Col.,  on  striped  hcmiouus,  i. 

,  in  pigeons,  to  blue  colour,  i. 

202. 

198. 

Potemogeton,  ii.  175. 
Pouchet,  on  the  colours  of  flat-fish, 

Rhododendron,  sterility  of,  ii.  7,  8. 
Richard,  Prof.,  on  Aspicarps,  ii.  209. 

i.  293. 

Richardson,  Sir  J.,  on  structure  of 

Prestwich,    Mr.,    on    English    and 

squirrels,  i.  216. 

French  eocene  formations,  ii.  105. 

,  on  fishes  of  the  southern  hemi- 

Proctotrupcs, i.  222. 

sphere,  ii.  164. 

Proteolepas,  i.  183. 
Proteus,  i.  173. 

Robinia,  grafts  of,  ii.  19. 
Rodents,  blind,  i.  170. 

Psychology,  future  progress  of,  ii. 

Rogers,  Prof.,  Map  of  N.  America, 

304. 

ii.  65. 

Pyrgoma,  found  in  the  chalk,  ii.  81. 

Rudimentary  organs,  ii.  255. 
Rudiments  important  for  classifica- 

tion, ii.  207. 

Q. 

Riitimeyer,  on  Indian  cattle,  i.  21  ; 

Quagga,  striped,  i.  201. 

ii.  10. 

Quatrefages,  M.,  on  hybrid  moths, 

S. 

ii.  9. 

Quercus,  variability  of,  i.  62. 
Quince,  grafts  of,  ii.  18. 

Salamandra  atra,  ii.  256. 
Saliva  used  in  nests,  i.  355. 
Salvin,  Mr.,  on  the  beaks  of  ducks, 

R. 

i.  287. 
Sageret.  on  grafts,  ii.  18. 

Rabbits,  disposition  of  young,  i.  328- 
Races,  domestic,  characters  of,  i.  18. 

Salmons,  males  lighting,  and  hooked 
jaws  of,  i.  108. 

Race-horses,  Arab,  i.  40. 

Salt  water,  how    far  injurious    to 

,  English,  ii.  140. 

seeds,  ii.  142. 

Radcliffe,  Dr.,  the  electrical  organs 

not  destructive  to  land-shells, 

of  the  torpedo,  i.  234. 

ii.  187. 

INDEX. 


STAR-FISHES. 


335 


Salter,  Mr.,  on  early  death  of  hybrid 

Shells,  fresh-water,  dispersal  of,  ii. 

embryos,  ii.  -.ri. 

173. 

Saurophagus  sulphuratus,  i.  220. 
Schacnt,  Prof.,  oil    Phyllotuxy,  i. 

,  of  Madeira,  ii.  180. 
,  land,  distribution  of,  ii.  180. 

270. 

,  land,  resisting  salt  water,  ii. 

Schiodte.  on  blind  insects,  i.  172. 

m. 

,  on  flat-fish,  i.  290. 

Shrew-mouse,  ii.  218. 

Sehlegel,  on  snakes,  i.  178. 

Silene,  infertility  of  crosses,  ii.  14. 

SchObI,  Dr.,  on  the  ears  of  mice,  i. 

Silliman,  Prof.,  on  blind  rat,  i.  171. 

268. 

Sireiiiu,  their  affinities,  ii.  108. 

Scott,  J.,  Mr.,  on  the  self-sterility  of 

Sitaris,  metamorphosis  of,  ii.  252. 

orchids,  ii.  7. 

Skulls  of  young  mammals,  i.  248: 

,  on  the  crossing  of  varieties  of 
verbascum,  ii.  38. 

ii.  235. 
Slave-making  instinct,  i.  336. 

Sea-water,    how    far    injurious    to 

Smith,  Col.   Hamilton,  on  btriped 

seeds,  IK  14:>. 

horses,  i.  200. 

not  destructive  to  land-shells, 

,  Mr.   Fred.,  on  slave-making 

ii.  187. 

ants,  i.  337. 

Sebright,  Sir  J.,  on  crossed  animals, 
i.  23. 

,  on  neuter  ants,  i.  360. 
Smitt,  Dr.,  on  the  Polyzoa,  i.*301. 

Sedgwick,  Prof.,  on  groups  of  spe- 
cies suddenly  appearing,  ii.  77. 
Seedlings  destroyed  by  insects,  i. 

Snake  with  tooth  for  cutting  through 
egg-shell,  i.  334. 
Somerville,  Lord,  on   selection  of 

83. 

sheep,  i.  35. 

Seeds,  nutriment  in,  i.  94. 

Sorbus,  grafts  of,  ii.  19. 

,  winged,  i.  181. 

Sorex,  ii.  218. 

,  means    of   dissemination,    i. 

Spaniel,  King  Charles's  breed,  i.  40. 

240,252;  ii.  146. 
,  power  of  resisting  salt  water, 

Specialisation  of  organs,  i.  152. 
Species,  polymorphic,  i.  54. 

ii.  143. 

,  dominant,  1.  '17. 

,    in    crops   and    intestines   ot 

,  common,  variable,  i.  66. 

birds,  ii.  146. 

in  large  genera  variable,  i.  6!>. 

,  eaten  by  fish,  ii.  146,  176. 
,  in  mud,  ii.  175. 

,  groups  of,  suddenly  appear- 
ing, ii.  77,  82. 

,  hooked,  on  islands,  ii.  181. 

beneath   Silurian  formations, 

Selection  of  domestic  products,  i.  "4. 

ii.  84. 

,  principle  not  of  recent  origin, 

successively  appearing,  ii.  89. 

i.  3'J. 

changing       simultaneously 

,  unconscious,  i.  39. 

throughout  the  world,  ii.  100. 

,  natural,  i.  97. 

Spencer,  Lord,  on  increase  in  size  of 

,  sexual,  i.  107. 

cattle,  i.  40. 

,  objections  to  term,  i.  99. 
natural,  has  not  induced  steri- 

  ,  Herbert,  Mr.,  on  the  first  steps 
in  differentiation,  i.  155. 

lity,  ii.  20. 

,  on  the  tendency  to  an  equili- 

Sexes, relations  of,  i.  108. 

brium  in  all  forces,  ii.  29. 

Sexual  characters  variable,  i.  191. 
selection,  i.  107. 

Sphex,  parasitic,  i.  336. 
Spiders,  development  of,  ii.  245. 

Sheep,  Merino,  their  selection,  i.  36. 

Sports  in  plants,  i.  11. 

,  two  sub-  breeds,  unintention- 
ally produced,  i.  41. 
,  mountain  varieties  of,  i.  93. 

Sprengel,  C.  C.,  on  crossing,  i.  119. 
,  on  ray-florets,  i.  180. 
Squalodon,  ii.  108. 

Shells,  colours  of,  i.  165. 

Squirrels,  gradations  in  structure,  i. 

,  hinges  of,  i.  240. 

SU. 

,  littoral,  seldom  embedded,  ii. 

Staffordshire,  heath,  changes  in,  i. 

58. 

87. 

,  fresh  -water,  long  retain  the 

Stag-beetles,  fighting,  i.  108. 

Barne  forms,  ii.  117. 

Star-fishes,  eyes  of,  i.  225. 

336 


STAR-FISHES. 


INDEX. 


Star-Fishes,  their  pedicellarias,  i.  299. 
Sterility  from   changed  conditions 
of  life,  i.  10. 

Thouin,  on  grafts,  ii.  19. 
Thrush,  aquatic  species  of,  i.  222. 
,  mocking,  of  the  Galapagos,  ii. 

of  hybrids,  ii.  3. 

192. 

•  ,  laws  of,  ii.  11. 
,  causes  of,  ii.  iiO. 

,  young  of,  spotted,  ii.  241. 
,  nest  of,  i.  364. 

,  from  unfavourable  conditions, 

Tliuret,  M.,  on  crossed  fuci,  ii.  15. 

ii.  26. 

Thwaites,   Mr.   on  acclimatisation, 

not  induced  through   natural 

i.  174. 

selection,  ii.  21. 

Thylacinus,  ii.  220. 

St.  Helena,  productions  of,  ii.  178. 

Tierra  del  Fuego,  dogs  of,  i.  328. 

St.  Hilaire,  Aug.,  on  variability  of 
certain  plants,  i.  272. 

,  plants  of,  ii.  169. 
Timber-drift,  ii.  145. 

.on  classification,  ii.  209. 

Time,  lapse  of,  ii.  51. 

St.  John,  Mr.,  on  habits  of  cats,  i. 

by  itself  sot  causing  modifica- 

325. 

tion,  i.  126! 

Sting  of  bee,  i.  256. 

Titmouse,  i.  220. 

Stocks,  aboriginal,  of  domestic  ani- 

Toads on  islands,  ii.  182. 

mals,  i.  22. 

Tobacco,  crossed  varieties  of,  ii.  38. 

Strata,  thickness  of,  in  Britain,  ii.  55. 

Tomes,  Mr.,  on  the  distribution  of 

Stripes  on  horses,  i.  199. 
Structure,  degreesof  utility  of,  i.  249. 

bats,  ii.  184. 
Transitions  in  varieties  rare,  i.  208. 

Struggle  for  existence,  i.  75. 
Succession,  geological,  ii.  89. 

Traquair,  Dr.,  on  flat-fish,  i.  293. 
Trautschold,on  intermediate  varie- 

  of  types  in  same  areas,  ii  121. 

ties,  ii.  66. 

Swallow,  one  species  supplanting 
another,  i.  93. 

Trees  on  islands  belong  to  peculiar 
orders,  ii.  182. 

Swaysland,  Mr.,  on  earth  adhering 
to  the  feet  of  migratory  birds,  ii. 

with  separated  sexes,  i.  123. 
Trifolium  pratense,  i.  90,  117. 

148. 

incarnatum,  i.  117. 

Swifts,  nests  of,  i.  355. 

Trigonia,  ii.  99. 

Swim-bladder,  i.  230. 

Trilo  bites,  ii.  83. 

Switzerland,  lake  habitations  of,  i. 

,  sudden  extinction  of,  ii.  99. 

20. 

Trimen,  Mr.,  on  imitatiug-insects, 

System,  natural,  ii.  204. 

ii.  224. 

T. 

Trimorphism  in  plants,  i.  55  ;  ii.  29. 
Troglodytes,  i.  864. 

Tuco-tuco,  blind,  i.  170. 

Tail  of  giraffe,  i.  245. 

Tumbler  pigeons,  habits  of,  heredi- 

  of  aquatic  animals,  i.  246. 

tary,  i.  327. 

,  prehensile,  i.  294. 

,  young  of,  ii.  248. 

,  rudimentary,  ii.  260. 

Turkey-cock,  tuft  of  hair  on  breast, 

Tanais,  dimorphic,  i.  55. 

i.  lib. 

Tarsi,  deficient,  i.  168. 

,  naked  skin  on  head,  i.  248. 

Tausch,  Dr.,  on  umbelliferfe,  i.  271. 

.  voung  of,  instinctively  wild, 

Teeth  and  hair  correlated,  i.  179. 

i.329. 

,   rudimentary,   in   embryonic, 
calf,  ii.  255,  292. 

Turnip    and    cabbage,    analogous 
variations  of,  i.  1  95. 

Tegetmeier,  Mr.,  on  cells  of  bees,  i. 

Type,  unity  of,  i.  260,  261. 

346,  352. 

Types,  succession  of,  in  same  areas, 

Temminck,  on  distribution  aiding 

ink 

classification,  ii.  211. 

Typotherium,  ii.  108. 

Tendrils,  their  development,  i.  305. 

Thompson,  Sir   W.,  on  the  age  of 

U1 

the  habitable  world,  ii.  83. 

. 

,  on  the  consolidation  of  the 

Udders  enlarged  bv  use,  i.  12. 

crust  of  the  earth,  ii.  275. 

,  rudimentary,  ii.  256. 

INDEX. 


337 


Ulex,  young  leaves  of,  ii.  241. 
Umbelliferaj,  flowers  and  seeds  of, 

Wagner,  Moritz,  on  the  importance 

of  isolation,  i.  1  L'7. 

i.  180.  ^ 

Wallace,  Mr.,  on  origin  of  species, 

,  outer  and  inner  florets  of,  i.  '270. 

i.  2. 

I'nity  of  type,  i.  260,261. 

,  on  the  limit  of  variation  under 

I'ria'laorymans,  i.  113. 

domestication,  i.  48. 

I'M-,  eiteete  of,  under  domestication, 

,  on  dimorphic  lepidoptcra,  i. 

i.  12. 

55,  862. 

,  effects  of,  in  a  state  of  nature, 

,  on  races  in  the  Malay  Archi- 

i. 167. 

pelago,  i.  58. 

Utility,  how  far  important  in  the 

,  on  the  improvement  of  the 

construction  of  each  part,  i.  2-iy. 

eye,  i.  227. 
,  on  the  walking-stick  insect,  i. 
284. 

,  on  laws  of  geographical  dis- 

Valenciennes, on  fresh-water  fish, 

tribution,  ii.  139. 

ii.  173. 

,  on  the  Malay  Archipelago,  ii. 

Variability   of  mongrels    and   hy- 

185. 

l.rids,  ii.  39. 

,  on  mimetic  animals,  ii.  224. 

Variation  under  domestication,  i.  8. 

Walsh,  Mr.  B.  D.,  on  phytophagic 

caused  by  reproductive  system 
being  affected  by  conditions  of 
life,  i.  10. 

forms,  i.  60. 
,  on  equal  variability,  i.  195. 
Water,  fresh,  productions  of,  ii.  171. 

under  nature,  i.  51. 

Water-hen,  i.  222. 

,laws  of,  i.  104. 

Waterhouse,    Mr.,    on    Australian 

,  correlated,  i.  13,  177,  248. 

marsupials,  i.  140. 

Variations  appear  at  corresponding 

,  on  greatly    developed    parts 

ages,  i.  16,  105. 

being  variable,  i.  185. 

analogous  in  distinct  species, 

,  on  the  cells  of  bees,  i.  343. 

i.  193. 
Varieties,  natural,  i.  50. 

,  on  general  affinities,  ii.  227. 
Water-ouzel,  i.  222. 

,  struggle  between,  i.  93. 
,  domestic,  extinction  of,  i.  134. 

Watson,  Mr.  H.  C.,  on    range  of 
varieties  of  British  plants,  i.  57, 

,  transitional,  rarity  of,  i.  208. 
,  when  crossed,  fertile,  ii.  34. 

73. 
,  on  acclimatisation,  i.  134. 

Varieties,  when  crossed,  sterile,  ii.37. 

,  on  flora  of  Azores,  ii.  149. 

,  classification  of,  ii.  215. 

,  on  Alpine  plants,  ii.  153. 

Verbascum,  sterility  of,  ii.  7. 
,  varieties  of  crossed,  ii.  38. 

,  on  rarity  of  intermediate  va- 
rieties, i.  212. 

Verlot.  M..  on  double  stocks,  i.  358. 

,  on  convergence,  i.  156. 

Verneuil,  M.  de,  on  the  succession 

,  on  the  indefinite  multiplica- 

of species,  ii.  103. 

tion  of  species,  i.  157. 

Vibracula  of  the  Polyzoa,  i.  301. 

Weale,  Mr.,  on  locusts  transporting 

Viola,  small   imperfect  flowers  of, 

seeds,  ii.  147. 

i.  2(59. 

Web  of  feet  in  water-birds,  i.  223. 

.  tricolor,  i.  90. 

Weismann,  Prof,  on  the  causes  of 

Virchow,  on  the  structure  of  the 
crystalline  lens,  i.  227. 
Virginia,  pigs  of,  i.  104. 

variability,  i.  8. 
,  on  rudimentary  organs,  ii.  260. 
West  Indian  Island's,  mammals  of. 

Volcanic  islands,  denudation  of,  ii. 

ii.  185. 

54. 
Vulture,  naked  skin  on  head,  i.  247. 

West  wood,  on  species  in  large  gen- 
era being  closely  allied  to  others, 

i.  71. 

W. 

,  on  the  tarsi  of  Engidfe,  i.  192. 

,  on  the  antennse  of  hymeno- 

Wadincr-birds,  ii.  175. 

pterous  insects,  ii.  207. 

Wagner,  Dr.,  on  Cecidomyia,  ii.  239. 

Whales,  i.  285. 

338 


INDEX. 


ZEUGLODOX. 


Wheat,  varieties  of,  i.  137. 

Woodward,  Mr.,  on  the  duration  of 

White  Mountains,  flora  of,  ii.  151. 

specific  forms,  ii.  66. 

Whittaker,  Mr.,  ou  lines  of  escarp- 

  ,  ou  Fyrgoma,  ii.  81.   . 

ment,  ii.  53. 

,  on  the  continuous  succession 

Wichura,  Max,  on  hybrids,  ii.  24, 

of  genera,  ii.  93. 

27,  41. 

,  on  the  succession  of  types,  ii. 

Wings,  reduction  of  size,  i.  169. 
•  of   insects    homologous   with 

121. 
World,  species  changing  simultane- 

branchiae, i.  231. 

ously  throughout,  ii.  100. 

,  rudimentary,   in    insects,    ii. 

W  reus,  nest  of,  i.  304. 

255. 

Wright,  Mr.  Chauncey,  on  the  gi- 

Wolf  crossed  with  dog,  i.  327. 

ratfe,  i.  278. 

of  Falkland  Isles,  ii.  1S3. 

,   on    abrupt    modifications,   i. 

Wollastou,  Mr.,  on  varieties  of  in- 

310. 

sects,  i.  59. 

Wyman,   Prof.,  on    correlation    of 

,  on  fossil  varieties  of  shells  in 
Madeira,  i.  65. 

colour  and  effects  of  poison,  i.  13. 
,  on  the  cells  of  the  bee,  i.  345. 

,  on  colours  of  insects  on  sea- 

shore, i.  165. 

Y. 

,  on  wingless  beetles,  i.  109. 
,  on  rarity  of  intermediate  va- 

Youatt, Mr.,  on  selection,  i.  35. 

rieties,  i.  212. 

,  on  sub-breeds  of  sheep,  i.  41. 

,  on  insular  insects,  ii.  178. 

,    on     rudimentary    horns    in 

,  on  land-shells  of  Madeira  nat- 

young cattle,  ii.  261. 

uralised,  ii.  193. 

Wolves,  varieties  of,  i.  111. 

Z. 

Woodcock  with  earth  attached  to 

leg,  ii.  148. 

Zanthoxylon,  i.  272. 

Woodpecker,  habits  of,  i.  220. 
,  green  colour  of,  i.  247. 

Zebra,  stripes  ou,  i.  199. 
Zeuglodon,  ii.  108. 

THE  END. 


University  of  California  , 

SOUTHERN  REGIONAL  LIBRARY  FACILITY 
Return  this  material  to  the  library 
from  which  it  was  borrowed. 


12 1988 


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